Concrete Block Calculator - Blocks, Mortar, Fill & Cost

How to use it

1. List the walls. One row per run: length, height, how many of that size, and how many ends are free rather than turning a corner. A 20 by 24 ft garage perimeter is two rows, not four: put 2 in the count. Dimensions take feet and inches, and the field accepts a comma or a period as the decimal mark so it reads the same in any browser.
2. Add the openings. Pick door, window or garage from the preset, or type your own size, then say how many and which wall each one sits in. The wall it sits in only matters for the drawing; the area comes off the total either way. Skip anything under about 8 sq ft: the cut waste around a small opening eats the saving.
3. Choose the block width. Four, 6, 8, 10 and 12 in are all nominal sizes, and every one of them lays on the same 8 by 16 in module, so the block count per square foot never changes. What changes is the weight, the cube count, the core volume and the price, and all four of those are editable fields with the typical value prefilled.
4. Set the cube count and the weight from your own yard. These are the two numbers other calculators bury as constants. Cube counts vary by plant: the same pallet is quoted as 90, 96 or 108 blocks in different parts of the country, and lightweight block runs about three quarters the weight of normal weight. One phone call sets both.
5. Set the waste factor. Five percent is the working default. The helper text pushes you to 8 or 10 percent once the job has three or more openings, because every jamb and head means cut block and the offcut from a jamb rarely fits anywhere else. Zero is allowed and the tool will tell you it is a mistake.
6. Pick how you are buying mortar. Premixed bags is the default at 12 blocks per 80 lb bag, which is one lower than Quikrete's rated 13 and deliberately so. Switch to masonry cement plus sand for the mix a mason actually orders: 3 bags of cement and 650 lb of sand per 100 blocks, shown in pounds, tons and 60 lb bags.
7. Choose the core fill mode. None for a garden wall. Reinforced cells for the common case, at a spacing between 16 and 48 in. Bond beams for a solid horizontal course. Cells plus beams for the full cage, and the tool takes the beam courses out of the cell height so nothing is counted twice. Every cell only when the plans say so.
8. Read the wall drawing. It shows your selected wall in running bond, with the openings cut out, the grouted cells shaded with a rebar dot in each course, the bond beam tinted across the top, the half blocks at the free ends and a dimension line under it. Change any input and the drawing changes with it.
9. Check the load against your truck. The weight line is a go or no go: it counts cubes, multiplies by your own weight per block and divides by the payload you type in. One cube of 8 in block is about 3,200 lb, which is more than any half ton pickup is rated to carry, so on most jobs the honest answer is delivery.
10. Edit the cost ledger to your own quotes. Blocks, half blocks, mortar, core fill, rebar, ladder wire, delivery and an optional labor rate, each a price you set with the real range printed beside it. The total divided by the wall area gives cost per square foot, which is the number to hold a contractor's bid against.

At a glance

• 20 ft x 4 ft garden wall, 8 in block, cells at 32 in: 80 sq ft, 6 courses. 95 blocks at 5 percent waste, 6 half blocks for the two free ends, 8 bags of 80 lb mortar. Nine grouted cells x 6 courses = 7.4 cu ft of core fill, so 13 bags. Four 10 ft sticks of rebar, 7 sticks of ladder wire. 3,420 lb, about 1.06 cubes. Materials $466.25, which is $5.83 a square foot.
• 20 x 24 ft garage stem wall, 2 ft high, cells and a bond beam: 88 lineal ft, 176 sq ft, 3 courses. 208 blocks, 18 bags of mortar, 38 grouted cells plus a fully grouted top course of 66 blocks. Core fill 28.6 cu ft = 1.06 cu yd, which crosses the ready-mix line. 19 sticks of rebar, 10 of ladder wire, 7,488 lb across 3 cubes. With delivery, $1,189.
• 12 x 16 ft shed, 8 ft walls, one door and two windows: 448 sq ft gross, 45 sq ft of openings, 403 net, 12 courses. At 8 percent waste for the cut around three openings: 490 blocks, 41 bags of mortar, 1.44 cu yd of core fill, 17,640 lb which is 8.8 tons and 6 cubes. Materials with delivery $2,287, or $5.68 a square foot of wall.

How the math works

Every number on this page comes off one chain and each link is visible in the result, so you can check it on paper. It starts with the laid module, which is the thing most people get wrong. A concrete block is not 8 by 16 in. A nominal 8 by 8 by 16 block actually measures 7-5/8 by 7-5/8 by 15-5/8, and the missing 3/8 in on each face is the mortar joint. Add the joint back and the module comes out at exactly 8 in high by 16 in long, which is 128 sq in, which is 0.889 sq ft of wall face per block. Turn that over and you get 1.125 blocks per square foot, or 113 blocks per 100 sq ft. Divide by the actual block size instead and you get 1.18 per square foot, which is about 2 percent too many and, worse, puts every opening and every course line in the wrong place. So the module here is fixed at 8 by 16 and the actual size is printed beside it. Area comes next. Each wall is length times height times how many of that size, summed. Openings are summed the same way and subtracted, clamped so they can never take more than 90 percent of the gross, which gives the net wall area. Blocks are net area times 1.125 times one plus the waste factor, rounded up: 80 sq ft is 90 blocks laid, and at 5 percent waste you order 95. Half blocks are separate and informational. In a running bond every second course starts half a block in, so any end that does not turn a corner needs a half block on every other course: the number is the course count divided by two, rounded down, per free end. A corner needs none, because the corner block itself turns the bond. Courses are the wall height in inches divided by 8, and the tool warns when that does not come out whole, because block does not split horizontally in any sensible way. Mortar is solved two ways because people buy it two ways. Premixed bags is the block count divided by the blocks per bag, rounded up, defaulting to 12 blocks per 80 lb bag and 9 per 60 lb bag. Quikrete rates the 80 lb bag at up to 13 blocks; the default here is one lower on purpose, because a 3/8 in joint laid by hand uses more mortar than a rated one and running out of mortar mid-course is worse than a spare bag. The other way is masonry cement plus sand, which is what a mason orders: 3 bags of cement and 650 lb of sand per 100 blocks, shown in pounds, in tons and as 60 lb bags for a small job. Core fill is where the arithmetic gets interesting. A cell is one vertical column of cores, and because a block has two cores, one cell running through one block holds half that block's core volume. An 8 in block holds 0.25 cu ft of core, so one cell-course is 0.125 cu ft. Cells across a wall are the length divided by the spacing, rounded up, plus one, because both ends get a cell: a 20 ft wall at 32 in on centre is 240 divided by 32, which is 7.5 spaces, so 8, so 9 cells. Nine cells through 6 courses at 0.125 is 6.75 cu ft, plus 10 percent grout waste is 7.43, which at 0.6 cu ft a bag is 13 bags. A bond beam is a whole course grouted solid, so its volume is the blocks in that course, which is the wall length times 0.75 blocks per lineal foot, times the full core volume. When you ask for cells and beams together, the cells are counted only through the courses below the beam, so the beam course is never charged twice. Past one cubic yard, about 45 bags, the tool stops recommending bags and hands the pour to ready-mix or a grout pump, with a link to the concrete calculator carrying the volume. Reinforcement follows the fill. Vertical rebar is one bar per grouted cell, so total feet is cells times wall height, plus a 10 percent lap allowance, divided by your stick length and rounded up: 9 cells at 4 ft is 36 ft, 39.6 with laps, so 4 sticks of 10 ft. Bond beam bars are the wall length times the beam courses times the bars per course, same lap and stick math. Ladder wire goes in every other bed joint, so the runs are the course count divided by two rounded down, times the wall length, plus 5 percent for the overlap at each splice, in 10 ft sticks. Weight is the block count times the weight per block, and cubes are the block count divided by your yard's cube count. Both of those are editable, because a cube is 90 blocks at one plant and 108 at another, and lightweight aggregate block runs about three quarters the weight of normal weight. The haul call then divides the total weight by the payload you type in. Finally the cost ledger, which is nothing but each quantity multiplied by a price you set: blocks, half blocks, mortar or cement and sand, core fill as bags or as cubic yards of ready-mix depending on which side of the threshold you are on, rebar by the stick, ladder wire by the stick, delivery as a flat fee and labor as an optional rate per square foot. The total divided by the net wall area is the cost per square foot, which is the figure that compares straight against the $15 to $30 a square foot that installed CMU work runs.

1. 1. Use the 8 x 16 in laid module, not the block you can measure

   A nominal 8 by 8 by 16 in block actually measures 7-5/8 by 7-5/8 by 15-5/8 in. The missing 3/8 in on each face is the mortar joint, and adding it back is what makes the module come out at exactly 8 in high by 16 in long. That is 128 sq in of wall face, which is 0.889 sq ft, which inverts to 1.125 blocks per square foot, or 113 per 100 sq ft. Every nominal width lays on that same face, so a 12 in block covers exactly as much wall as a 4 in one and the count per square foot never changes with thickness. Measure the block with a tape and divide by 15.625 by 7.625 instead and you get 1.18 per square foot: about 2 percent too many blocks, and every course line and opening head in the wrong place.

2. 2. Take off the walls, then take the openings out

   Measure each run and give it its own row, with a count for repeats: a 20 by 24 ft garage perimeter is two rows of 2, not four rows of 1. Measure outside-to-outside on one wall of a corner and inside-face on the wall that meets it, so the corner block is counted once rather than twice. Then subtract the openings. A 12 by 16 ft shed with 8 ft walls is 56 lineal ft, so 448 sq ft gross; take out a 3 by 7 door and two 3 by 4 windows, which is 45 sq ft, and the net is 403. Openings under about 8 sq ft are usually not worth subtracting, because the cut waste around the jambs is about what you saved.

3. 3. Multiply out the blocks and add the waste

   Blocks are net area times 1.125, times one plus the waste factor, rounded up. On the 80 sq ft reference wall: 80 times 1.125 is 90 laid, times 1.05 is 94.5, so order 95. Five percent is the working default and it covers breakage in transit, which alone runs 2 to 3 percent, plus the odd cut. Push it to 8 or 10 percent when the job has three or more openings, several corners, or a lot of short returns, because every jamb, head and return means cut block and a cut piece rarely fits anywhere else. Ordering flat with no waste is the one choice that reliably goes wrong, and it goes wrong on the last course with the yard closed.

4. 4. Count courses, and count the half blocks the bond needs

   Courses are the wall height in inches divided by 8. A 4 ft wall is 48 in, so 6 courses. If it does not divide evenly the tool says so, because block does not split horizontally: your options are to change the height, or to plan a 4 in high course or a solid cap to make up the difference. Half blocks are a separate count. In a running bond every second course starts half a block in, so any end that does not turn a corner needs a half block on every other course: courses divided by two, rounded down, per free end. A 6 course wall with both ends free needs 6 half blocks; the same wall running into corners at both ends needs none, because the corner block itself turns the bond.

5. 5. Solve the mortar the way you are actually buying it

   Premixed bags: 95 blocks divided by 12 blocks per 80 lb bag is 7.9, so 8 bags. The default of 12 is deliberately one below Quikrete's rated 13, because a hand-laid 3/8 in joint uses more than a rated one, and a spare bag costs $9 while running out mid-course costs an afternoon. Masonry cement plus sand: 3 bags of cement and 650 lb of sand per 100 blocks, so 95 blocks is 3 bags of cement and 618 lb of sand, which is 0.31 tons or 11 bags of 60 lb sand. Below about 200 blocks premixed is simpler and barely costs more; above that, cement and sand is meaningfully cheaper and lets you mix to the consistency the day needs.

6. 6. Grout the cells, and stop counting the beam twice

   A cell is one vertical column of cores. A block has two cores, so one cell through one block holds half that block's core volume: 0.125 cu ft for an 8 in block. Cells across a wall are length divided by spacing, rounded up, plus one for the far end, so 240 in at 32 in on centre is 8 spaces and 9 cells. Nine cells through 6 courses at 0.125 cu ft is 6.75 cu ft, plus 10 percent grout waste is 7.43, which is 13 bags at 0.6 cu ft each. A bond beam is a whole course grouted solid, so it is the wall length times 0.75 blocks per lineal foot times the full core volume: an 88 ft perimeter is 66 blocks, times 0.25, is 16.5 cu ft for the beam alone. Ask for cells and beams together and the cells are only counted through the courses below the beam, so the beam is never charged twice.

7. 7. Draw the ready-mix line at one cubic yard

   One cubic yard of core fill is 27 cu ft, which is 45 bags of 80 lb mix. Under that line, bags win: no short-load fee, no truck to schedule, and you can pour a cell at a time. Over it, bags stop making sense fast. The 88 ft stem wall above comes to 28.6 cu ft, which is 1.06 cu yd, which is 48 bags to buy, carry, cut open and mix by hand for one afternoon of grouting. That is the point where a ready-mix grout with a short-load fee, or a grout pump, is both cheaper and far less work. When the tool crosses that line it swaps the ledger line from bags to cubic yards and sends the volume to the concrete calculator to price the pour properly.

8. 8. Take off the steel, then weigh the load

   Vertical rebar is one bar per grouted cell: cells times wall height, plus 10 percent for lap splices, divided by the stick length. Nine cells at 4 ft is 36 ft, 39.6 with laps, so 4 sticks of 10 ft. Ten foot sticks fit in a pickup, 20 ft sticks mean fewer splices and a trailer. Bond beam bars are wall length times beam courses times bars per course, and 10 and 12 in walls usually take two. Ladder wire goes in every other bed joint: 6 courses is 3 runs, so 3 times 20 ft is 60 ft, plus 5 percent overlap, which is 7 sticks of 10 ft. Then weigh it: 95 blocks at 36 lb is 3,420 lb, which is 1.06 cubes at 90 to a cube, and 3 trips against a 1,500 lb pickup payload. That is why block gets delivered.

Worked scenarios, start to finish

Real jobs with the numbers carried all the way through, so you can see how the estimate is built and check your own figures against them.

The judgement calls a pro makes

Decisions the tool cannot make for you, and how someone who does this for a living thinks them through.

Measuring a corner so the block is counted once

Two walls meeting at a corner share the block that turns the bond, and the easiest way to count it twice is to measure both walls outside-to-outside. The fix is a convention: measure one wall outside-to-outside and the wall that meets it from the inside face, all the way round. On a 20 by 24 ft garage that is the difference between 88 lineal ft and roughly 90.7, which is about 2 blocks a course, which over 3 courses is 6 blocks. Small on this job, real on a tall one, and it compounds with the waste factor. The same convention keeps the corner in the drawing where it belongs.

How much waste to actually carry

Five percent is right for a plain run with square ends and nothing to cut around. Push to 8 percent once there are three or more openings, and to 10 percent on a job full of short returns and corners, like a BBQ island. The reason is not breakage, it is geometry: a block cut to fit a jamb leaves an offcut of the wrong length for anything else, so cut waste is genuinely lost in a way that transit breakage is not. Zero waste is allowed here and it is always wrong: 2 to 3 percent of a pallet arrives chipped, cracked or with a broken corner, before you cut anything at all.

Confirming the cube count before you divide by 90

Ninety blocks to a cube is the number everyone quotes for 8 in block, and it is right at plenty of plants and wrong at plenty of others: 90, 96 and 108 all ship, and the count changes with width as well as with the plant. It matters because the cube is the unit the yard prices and loads in, so a 208 block order is either three cubes short-loaded or two cubes plus a loose 28, and those cost different money and arrive on different trucks. Ask the yard, then set the field here. The same call gets you the weight per block, which is the number the haul decision rests on.

Where to draw the line between bagged grout and ready-mix

The threshold in this tool is one cubic yard, which is 45 bags of 80 lb mix, and it is a good working line rather than a rule. Below it, bags win on cost and convenience, because a ready-mix short load carries a fee of $60 to $150 on top of the yard price and you have to be ready when the truck is. Above it, bags lose fast: a yard and a half is 65 bags, which is well over a ton of material to move, open and mix in an afternoon with the grout going off while you work. If you are already ordering a truck for the footing, ask about grout in the same delivery. And whatever you order, ask for a fine or pea-gravel core-fill mix, not a coarse-aggregate concrete.

Whether the wall needs grouted cells at all

A low garden wall, under about 3 ft with nothing bearing on it, is commonly laid with dry cores and nothing but ladder wire. Above that, most jurisdictions want vertical bars in grouted cells at a designed spacing, a footing sized to the soil and the frost depth, and often a permit and a stamped detail. The tool will let you build a 6 ft freestanding wall with no fill and will warn you about it, because that is a real wall people really build and it is also how walls fall over. The honest position: the spacings and beam counts offered here are prescriptive reference, the sort of thing a code table would give you, and your plans or your building department govern.

Type S or Type N mortar

Type N is the general purpose mix for above-grade, non-structural work: garden walls, veneers, partitions. It is softer than the block, which is what you want, because a crack then runs through the joint where it can be repointed rather than through the block where it cannot. Type S is stronger, bonds better and stands up to lateral load and moisture, which makes it the choice below grade, for foundation and stem walls, retaining stems and anything structural. Both come premixed in 80 lb bags at similar prices, so this is a specification decision rather than a budget one. If the wall is holding back soil or carrying a floor, use S.

Whether to pick up or take the delivery

Run the arithmetic on your own truck rather than on a forum's. A cube of 8 in block is roughly 90 blocks at 36 lb, which is about 3,240 lb, and the payload sticker inside the driver's door of a typical half ton pickup reads 1,500 to 2,000 lb including passengers. So a cube is not a pickup load; it is closer to two full loads, and it needs a forklift at both ends anyway. Delivery on a boom truck runs about $75 to $150 in most markets, and the driver will set the cubes where you are laying rather than at the end of the drive. On any order past a few hundred blocks the fee is not the expensive part of the day.

Wet-setting the first course or bedding it on cured concrete

If you are pouring the footing yourself, the fastest path is to set the first course into the footing while the concrete is still green, which locks the block in and saves a bed joint. It is unforgiving: you get one shot at level and line, and you are working against the concrete setting. Bedding on cured concrete is the normal way. Snap your lines, dampen the footing so it does not suck the water out of the mortar, and lay a full mortar bed thick enough to take up the footing's own irregularity. The first course is the whole wall: an eighth of an inch out of level at course one is an eighth of an inch out at course twelve, plus whatever you added on the way up.

Common mistakes, and the fix

• × Using the actual 15-5/8 by 7-5/8 in block size instead of the 16 by 8 in laid module.

  ✓ Divide by the module, not by the block. The 3/8 in mortar joint on two faces is what makes the module exactly 8 by 16, so the count is 1.125 blocks a square foot. Use the actual block and you get 1.18, which overcounts by about 2 percent and, worse, mis-positions every course line and every opening head on the drawing.

• × Assuming a pickup can haul a cube of block.

  ✓ A cube of 8 in block is about 90 blocks at 36 lb, so roughly 3,240 lb. The payload sticker inside a half ton's driver door usually reads 1,500 to 2,000 lb including passengers. That is two trips, not one, and the cube needs a forklift at both ends. Take the delivery, and set your own payload in the tool so the haul line is about your truck.

• × Buying standard concrete mix with 3/4 in stone for core fill.

  ✓ Ask for a core-fill or grout mix with fine or pea-gravel aggregate. Coarse stone bridges across a 5 in cell and leaves a void exactly where the bar needed grout, which is worse than not filling at all because you cannot see it. If you are mixing bags, a bagged core-fill or a sand mix with pea gravel pours and consolidates properly.

• × Forgetting the lap splice allowance on rebar.

  ✓ Add 10 percent, which this tool does automatically. Bars lap rather than butt, and a typical lap for a #4 bar is 25 to 30 in, so a 4 ft wall with 10 ft sticks loses most of a foot at every splice. Order sticks, not exact footage, and cut on site.

• × Counting a bond beam course twice when you also grout cells.

  ✓ Grout the vertical cells only through the courses below the beam. This tool takes the beam courses off the cell height automatically, so the 88 ft stem wall counts 38 cells through 2 courses plus one solid 66 block beam, not 38 cells through all 3. Done by hand it is the single most common double count in a block takeoff.

• × Measuring wall height in courses of 8-5/8 in, or in whole feet.

  ✓ A course is exactly 8 in, block plus joint. Height in inches divided by 8 gives the course count, so 4 ft is 6 courses and 8 ft is 12. If your height does not divide by 8, block will not make it up: change the height, or plan a 4 in high course or a solid cap course to close the gap.

• × Treating segmental retaining blocks and CMU as interchangeable.

  ✓ They are different products with different math. Segmental retaining wall block is dry-stacked with a lip or a pin, no mortar, no cores to grout, and its own setback and geogrid rules. This page will overcount mortar wildly for one and has no way to size the geogrid. Use a retaining wall calculator for those.

• × Ordering exactly the calculated block count with no spares.

  ✓ Carry at least 5 percent, and 8 to 10 percent on a job with several openings. Transit breakage alone is 2 to 3 percent before you cut anything, and a second delivery for twelve blocks costs another trip fee and a day. Leftover block, unlike leftover sod, keeps forever in the corner of the yard.

Material and unit specifics

Nominal size, actual size and why both matter

Block is sold by nominal size and made 3/8 in under it in every direction, so the mortar joint brings it back. A nominal 4 in is 3-5/8 by 7-5/8 by 15-5/8; a 6 in is 5-5/8; an 8 in is 7-5/8; a 10 in is 9-5/8; a 12 in is 11-5/8. The height and length are the same across all five, which is why the count per square foot is always 1.125. Use nominal sizes when you are laying out a wall and counting blocks, because the module is what the wall is built on. Use actual sizes when something has to fit: a 12 in wall gives you 11-5/8 in of bearing, not 12, and an opening framed to a nominal dimension will be 3/8 in tight.

Weight by width, normal and lightweight

Normal weight block runs roughly 27 lb for a 4 in, 32 for a 6 in, 36 for an 8 in, 44 for a 10 in and 52 for a 12 in. Lightweight aggregate versions run about three quarters of that, so an 8 in lightweight is nearer 28 lb, and they cost 10 to 20 percent more per block. On a 500 block job that is roughly 4,000 lb less to lift, one block at a time, which is worth more than it looks by the fifth course. Every one of these is a typical figure and every one of them is an editable field here, because the number that matters is your supplier's, printed on their spec sheet.

Cubes, and why 90 is not a constant

Block ships banded in cubes, and the count per cube varies by plant and by width. Common counts are 90 or 96 for 8 in, 108 for 6 in, 120 for 4 in, 72 for 10 in and 60 for 12 in, all landing in a similar 3,100 to 3,500 lb band because the cube is sized to what a forklift and a flatbed can handle. That band is the useful sanity check: if your cube count times your weight per block is way outside it, one of the two numbers is wrong. Confirm it with the yard and set it here, because the cube is the unit they price and load in.

Grout yield: how many blocks a cubic yard fills

One cubic yard is 27 cu ft, and dividing by the core volume of a block gives the fill rate. At the core volumes used here that is about 159 blocks for a 6 in, 108 for an 8 in, 82 for a 10 in and 56 for a 12 in. Published tables run a little either side of those, roughly 155 to 160 for 6 in, because core geometry varies by manufacturer. A 4 in block is not on the list: its cores are too small to grout or to take a bar. The practical use of the table is a sense check before you order, because doubling the wall thickness roughly doubles the grout.

Type S against Type N mortar

Type N is the general purpose mix, roughly 750 psi, for above-grade non-structural work: garden walls, veneer, partitions. Being softer than the block is a feature, because cracking runs through the repointable joint rather than the block. Type S is roughly 1,800 psi, bonds better and takes lateral load and moisture, so it is the mix for below grade, foundations, stem walls, retaining stems and anything structural. Both come as 80 lb premixed bags at similar money, and both cover about 12 blocks a bag laid with a 3/8 in joint. If the wall retains soil or carries a floor, use S.

Hollow, solid, cap and bond beam block

A standard stretcher is hollow with two cores and a web between them. A corner or end block has one flat end so the end shows a finished face. A half block is exactly what it sounds like and is what a running bond needs at every free end, every other course. A solid cap block, usually 2 to 4 in thick, closes the top of a wall and sheds water. A bond beam block has a knocked-out or lowered web so a horizontal bar can run through the course before it is grouted solid. Order caps and bond beam block by the piece with the main order: they are stocked in smaller numbers and a special trip for twenty of them wastes a day.

Rebar, ladder wire and what they each do

Vertical rebar, usually #4 which is half an inch, goes in the grouted cells and ties the wall to the footing, resisting the sideways push of wind or soil. It laps rather than butts, typically 25 to 30 in for a #4, which is where the 10 percent allowance comes from. Horizontal bars sit in bond beam courses and tie the wall together along its length. Ladder or truss joint reinforcement is a light welded wire that goes in the bed joint every other course, 16 in vertically, and it is doing a different job: it controls shrinkage cracking rather than carrying load. It comes in 10 ft sticks, laps about 6 in at splices, and it is the cheap line item everyone forgets to order.

What block actually costs in 2026

An 8 in standard block runs $1.50 to $3.50 depending on region and supplier, with $2.25 a fair planning figure; 12 in runs $3 to $5, 6 in around $1.80 to $3, 4 in around $1.50 to $2.60. Premixed mortar is $7 to $12 an 80 lb bag, masonry cement about $11, masonry sand about $6 for 60 lb bagged or roughly $40 a ton bulk. Bagged core fill is about $6.50, ready-mix grout $150 to $220 a cubic yard plus a short-load fee. Rebar is around $1.10 a foot for #4, ladder wire about $0.55 a foot. Delivery is $75 to $150. Installed CMU work, block plus mortar plus labor, typically runs $15 to $30 a square foot of wall, which is the number the ledger here is worth comparing against.

Footings, frost and what is out of scope here

A block wall is only as good as what it sits on. The usual prescriptive starting point is a footing twice the wall width and at least as deep as the wall is thick, with its bottom below the local frost line, on undisturbed soil. For an 8 in wall that is commonly a 16 by 8 in trench footing, which is what the helper here defaults to. The helper gives you the volume and a bag count and then hands you to the concrete calculator, because a footing of any size is a ready-mix pour and sizing it properly is that tool's job. Frost depth, soil bearing, reinforcement in the footing and drainage behind a retaining stem are all local code questions, not arithmetic.

Reading your result

Read the headline as an order, not a total. The block count already carries your waste factor, so it is what you ask the yard for, and the half block line beside it is a separate item they have to pick separately. If the count lands just under a cube, look at the cube line before you order: a yard that has to break a cube for the last twelve blocks may charge you differently, and topping up to the full cube often costs less than the handling. The stat row under the headline is the rest of the shopping list in one glance, and mortar is the one to sanity check, because it is the material people run out of. The core fill block is where most of the judgement lives. The volume in cubic feet is the honest number and the bag count is the convenience number, and the tool switches which one it recommends at one cubic yard because that is where the work stops being reasonable. If you are just over the line, look at what is pushing you there: it is almost always a bond beam, because a solid course of 66 blocks holds more grout than 38 vertical cells do. If you are just under it, remember that bags let you grout one lift at a time on your own schedule. Either way the volume is the number to carry over to the concrete calculator, not the bag count. The weight line is a go or no go rather than trivia. It multiplies your own weight per block by the count and divides by the payload you typed, so if it says delivery, it is saying your truck cannot legally or safely take it, not that delivery is more convenient. The cube figure is what the yard will load, so a job at 1.06 cubes is genuinely two cubes on the truck with most of the second one coming home unopened. The cost ledger is a planning ledger and nothing more: every line is a quantity from the geometry multiplied by a price you typed, so it is exactly as good as the prices you put in. Its most useful output is the cost per square foot at the bottom. Materials on a plain garden wall land around $4 to $6 a square foot, and installed CMU work runs $15 to $30, so the gap between those two numbers is what your own labor is worth on this job. That comparison, rather than the block count, is the decision most people are actually making on this page. Finally, treat every structural figure here, cell spacing, bond beam count, footing size, maximum unreinforced height, as prescriptive reference to check locally. The arithmetic is the same everywhere. The code is not.

Limitations

• This is a materials planning estimate, not a quote and not an engineering design. Cell spacing, bond beam counts, footing sizes and maximum unreinforced heights are prescriptive reference to confirm with your local building department or the engineer on your plans.
• Mortared concrete block (CMU) only. Dry-stack segmental retaining wall block is a different product with no mortar, no groutable cores and its own setback and geogrid rules, and this page will overcount mortar badly for it.
• Block weights, cube counts, core volumes and every price are typical US figures for 2026 and editable for exactly that reason. Cube counts in particular vary by plant, so confirm yours before you divide by 90.
• Openings are subtracted by area and placed evenly along the wall they belong to for the drawing. The tool does not know where you intend to put them, and it does not size lintels, which depend on the span and the load above.
• Mortar coverage assumes a standard 3/8 in joint laid by hand on a face shell bed. A full bed, a wider joint, or a very hot dry day all use more, which is why the default is one block per bag below the rated figure.
• Core fill volumes use one core volume per block width. Real block varies by manufacturer and by whether the cores are tapered, so treat the grout figure as a good working number rather than an exact one and order a little over.
• Footings, drainage, waterproofing, lintels, control joint detailing and anchorage to a slab or a frame are out of scope beyond the volume helper and the cross-link to the concrete calculator.
• Imperial units, in feet, inches, square feet, cubic feet, cubic yards and pounds, consistent with the rest of the site.

Frequently asked questions

How many concrete blocks do I need per square foot of wall?

You need 1.125 blocks per square foot of wall, which is about 113 blocks per 100 sq ft before waste. The number comes from the laid module rather than the block: a nominal 8 by 8 by 16 in block actually measures 7-5/8 by 7-5/8 by 15-5/8, and adding the 3/8 in mortar joint back brings the module to exactly 8 in high by 16 in long, which is 0.889 sq ft of face. One divided by 0.889 is 1.125. Every nominal width lays on that same 8 by 16 face, so a 12 in block covers exactly as much wall as a 4 in one and the count per square foot never changes with thickness. Add 5 percent waste for a plain wall and 8 to 10 percent for a job with several openings, so 100 sq ft of plain wall is 113 laid and 119 ordered.

How many blocks will 1 yard of concrete fill?

About 108 standard 8 in blocks, because a cubic yard is 27 cu ft and an 8 in block holds roughly 0.25 cu ft of core. The same arithmetic gives about 159 blocks for a 6 in, 82 for a 10 in and 56 for a 12 in, and a 4 in block is not on the list because its cores are too small to grout or to take a bar. Published tables vary a little either side of those figures, roughly 155 to 160 for 6 in for example, because core geometry differs between manufacturers, so check your block's spec sheet if the order is large. Note that these are fully filled blocks. If you are only grouting the cells that carry rebar, one cell through one block is half the block's core volume, so a cubic yard goes roughly twice as far.

How much sand and cement do I need for 100 blocks?

About 3 bags of masonry cement, 70 to 80 lb each, plus roughly 650 lb of masonry sand per 100 blocks laid with a standard 3/8 in joint. That 650 lb is about a third of a ton, or 11 bags of 60 lb sand if you are buying it bagged rather than by the ton. If you would rather buy premixed mortar, the equivalent is 8 to 9 bags of 80 lb mix per 100 blocks, working at 12 blocks a bag. Quikrete rates an 80 lb bag at up to 13 blocks; planning at 12 is deliberate, because a hand-laid joint uses more than a rated one and a spare bag costs $9 while running out mid-course costs an afternoon. Below about 200 blocks, premixed is simpler and barely costs more. Above that, cement and sand is meaningfully cheaper.

How much does a concrete block weigh?

A standard 8 by 8 by 16 in normal weight block weighs about 33 to 38 lb, with 36 lb a fair planning figure. Lightweight aggregate versions of the same block run around 28 lb and cost 10 to 20 percent more. Across the widths, normal weight runs roughly 27 lb for a 4 in, 32 for a 6 in, 36 for an 8 in, 44 for a 10 in and 52 for a 12 in. The number that actually decides your day is the cube: 90 blocks of 8 in at 36 lb is about 3,240 lb, and cube counts are chosen so most widths land in a similar 3,100 to 3,500 lb band. That is well past the 1,500 to 2,000 lb payload printed inside the driver's door of a typical half ton pickup, which is why block gets delivered on a boom truck rather than fetched.

What is the difference between a cinder block and a concrete block?

For anything you are buying today, nothing. Both terms describe a concrete masonry unit, a CMU. The name cinder block comes from an older product made with coal cinders as the aggregate, which was lighter, weaker and largely gone from the market by the 1950s and 60s as coal-fired power and steel production stopped supplying cinders. Modern block is made with sand, gravel and Portland cement, and the lightweight versions use expanded shale, clay or slate rather than cinders. The colloquial name survived, so a US yard will sell you the same grey two-core block whichever word you use. Same nominal sizes, same 8 by 16 in laid module, same 1.125 blocks per square foot, same math on this page.

Do I need to fill the cores of a block wall with concrete?

Usually not all of them. For most reinforced walls you grout only the cells that carry a vertical bar, at whatever spacing the plans or the code table give you, plus any bond beam courses, which are whole courses grouted solid with horizontal bars in them. A low garden wall, under about 3 ft with nothing bearing on it, often needs no fill at all beyond ladder wire in the bed joints. Fully grouting every cell is done when a design calls for it, for load, for lateral resistance, for fire or sound rating, and it is heavy and expensive: an 8 in wall fully grouted takes a cubic yard of grout for every 108 blocks. What decides this is your local code and your plans, not a rule of thumb, so treat the modes offered here as prescriptive reference and confirm the spacing with your building department.

How much does a cinder block wall cost?

For materials, plan on $4 to $8 per square foot of wall depending on the block width, whether you are grouting cells and how much reinforcement is in it. The 24 ft garden wall worked through on this page comes to $397 for 96 sq ft, which is $4.14 a square foot with no core fill. The 12 by 16 ft shed, with cells, a bond beam and delivery, comes to $2,287 for 403 sq ft, which is $5.68. Installed is a different order of magnitude: professional CMU work typically runs $15 to $30 per square foot all in, because laying block is slow, heavy, skilled work and the labor is most of the bill. The gap between the two, roughly $10 to $25 a square foot, is what your own time is worth on the job, and that is the comparison the cost ledger here is built to let you make.

How many blocks are in a cube or a pallet?

For 8 in block the usual answer is 90, and it is genuinely not a constant: 90, 96 and 108 all ship depending on the plant. Other widths run roughly 120 for a 4 in, 108 for a 6 in, 72 for a 10 in and 60 for a 12 in, and the counts are chosen so a cube lands in a manageable 3,100 to 3,500 lb band for a forklift and a flatbed. The reason to confirm it before ordering is that the cube is the unit the yard prices and loads in. A 208 block order is either three cubes short-loaded or two cubes plus 28 loose, and those arrive differently and cost differently. Ask the yard the count, then set it in the tool, because every weight, cube and haul figure downstream moves with it.