Retaining Wall Calculator - Blocks, Base, Drainage & Cost

How to use it

1. Call your building department and 811 before anything else. Permits, setbacks from a property line and the location of buried utilities all change what you are allowed to build, and none of them are arithmetic. 811 is free and takes a few days, so start it now and measure while you wait.
2. Measure the wall in runs. Length and exposed height for each straight or curved run, feet and inches in their own boxes so 12 ft 7 in never becomes 12.7 ft. Mark a run as curved and it carries the higher waste rate, and tick the corner box where two runs meet so the overlap comes off once instead of being counted twice.
3. Pick and then measure the block. The three presets are the real classes on a pallet: 12 by 4 by 8 in garden block, 16 by 6 by 10 in standard SRW, 18 by 8 by 12 in large hollow. Catalog names are marketing, so put a tape on the block you are actually buying and type what it says. Every dimension, weight and price is editable.
4. Check the cap row. Caps are a separate SKU on a separate pallet and they count toward the exposed height, so switching them off changes the course count, not just the shopping list. The adhesive is worked from the linear feet of bead at the coverage on the tube, not from the size of the wall.
5. Read the burial, do not set it. The tool buries the first course by the larger of 1 in per foot of exposed height and half a course, then builds to the next whole course, and prints what that really came to. On the seeded wall the rule asks for 2 in and the wall ends up buried 3, because you cannot lay three quarters of a block.
6. Set the base trench and the drainage column. The trench seeds at the block depth plus 12 in by 6 in deep, and the column at 12 in of clean stone with 6 in of topsoil over it. Gravel is ordered loose and finishes compacted, so the base line is 20 percent bigger than the hole. Every one of those figures is editable with its source printed beside it.
7. Check the weight before you plan the trip. The tool adds the block, the caps and both tonnages of stone and divides by your truck's payload. A 40 ft wall at 3 ft is 13 tons of material, which is eighteen pickup loads and the reason most of these orders get delivered.
8. Edit the prices and read the ledger. Every line is your local number, the ledger totals from the rounded line costs so the column adds up to the cent, and the per linear foot figure sits beside the published installed range so you can see what your own labour is worth.

At a glance

• 20 ft of garden wall block, 2 ft exposed: 6 courses built to 27 in, 3 in buried, 126 blocks, 21 caps, 1.04 t base, 1.81 t stone, $765.41 or $38.27 a linear foot
• 40 ft of standard SRW block, 3 ft exposed: 6 courses to 39 in, 189 blocks, 42 caps, 2.28 t base, 5.70 t stone, 13 tons of material, $2,087.98 or $52.20 a linear foot
• 15 ft at 5 ft exposed: Over the design line: the page switches to a budget frame, names geogrid as an output it will not compute, and routes you to a stamped design
• 24 ft of 6x6 timber, 2 ft exposed: 6 courses of 5.5 in timber built to 33 in, 22 timbers with the deadmen, 42 spikes, 6 rebar pins, $921.95
• An L shape, 24 ft at 2.5 ft plus a 12 ft return: The corner overlap comes off as its own signed row: 130 blocks and 37 caps, not the 134 the two runs add up to
• The same 20 ft wall with no cap row: 7 courses instead of 6 and 147 blocks instead of 126, because the cap was covering 3 in of the burial

How the math works

Lengths are held in inches and volumes in cubic feet, so the divide by 27 happens once at the end and feet-and-inches entry stays exact. Courses come first, because everything else hangs off the built height. The buried depth is the larger of 1 in per foot of exposed height and half a course, per the Allan Block residential manual; the field courses have to cover exposed height plus burial minus the cap height, rounded up to a whole course; and the burial that actually results is the built height minus the exposed height, which is printed rather than hidden. On the seeded wall that is 24 + 2 - 3 = 23 in of field, 6 courses of 4 in, 27 in built and 3 in really buried. Blocks are courses times the run divided by the block length, netted against any corner overlap, rounded up ONCE at project level because a cut block is reusable at the opposite end of a running bond, then waste at 5 percent straight or 10 percent curved. Caps run the same way off the cap length. The base is the run times the trench width times the trench depth, converted to cubic yards, multiplied by 1.2 because gravel is ordered loose and finishes compacted, then by 1.4 tons per cubic yard, the same density our gravel and cubic yard pages use. The drainage column is the run times the column width times the built height less the topsoil cap, at the same density, plus the core fill volume on a hollow block. Pipe is the run in 10 ft sticks, fabric is the run times the column height plus the wrap in 150 sq ft rolls, and adhesive is the linear feet of cap bead divided by the 13.6 ft a 10 oz cartridge of PL 500 covers at a 3/8 in bead. One consequence worth knowing, because the tool prints it: on a low wall the cap height happens to pay for the burial, so a face-area count lands on the same course. Above roughly 3 ft of exposed height the 1 in per foot rule outruns a 3 in cap and the wall gains a whole course a block count never sees. Segment rows are apportioned against the printed total by largest remainder, corner overlaps included as signed negative rows, and the money ledger totals from the rounded line costs, so every column on the page adds up to the figure sitting under it.

1. 1. Call the building department and 811, before you measure

   This is a real step, not a footnote. Most jurisdictions want a permit above 4 ft of exposed height and many want one lower than that, and a wall on or near a property line has its own setback rules. 811 is the free national call-before-you-dig number: you call or file online, the utilities come out and mark gas, electric, water and communications, and it usually takes two to three working days. A base trench is only 6 in deep but the drainage column and the deadmen go deeper, and a wall is the kind of permanent structure a surveyor's pin argument gets expensive over.

2. 2. Measure the wall in runs, not as one number

   Walk the wall and write down each straight or curved run with its own length and its own exposed height, measured from where the finished grade in FRONT of the wall will be to where the top of the cap will sit. Height almost always changes along a run that follows a slope, so split it where it steps and let each piece carry its own course count. Where two runs meet at a corner, tick the corner box: measured to the outside of the corner both runs include the same block, and the tool takes one block depth back out as a signed row so the count is right instead of generous.

3. 3. Put a tape on the block you are actually buying

   Segmental wall block is not standardised the way brick or CMU is. Two blocks both sold as a standard 16 in unit can be 6 in or 8 in tall and 10 in or 12 in deep, and the depth drives the base trench width, the drainage column position and the setback the wall leans back at. The presets here are the three honest classes, 12 by 4 by 8, 16 by 6 by 10 and 18 by 8 by 12, and all three are editable. Measure one on the pallet, or read the spec off the manufacturer's own sheet, and type it.

4. 4. Solve the courses with the first course buried

   The buried course is what keeps the toe of the wall from kicking out and what stops erosion undercutting it. The rule this tool uses is the larger of 1 in of buried block per 1 ft of exposed height and half a course, and then it rounds up to a whole course, because a block is a block. The number to check is the built height, not the course count: a wall standing 2 ft above grade is built 27 in tall in 4 in block, and 27 in of block is what you are buying.

5. 5. Count the blocks once, then add waste

   Courses times the run over the block length gives the exact count. That gets rounded up once, at project level, rather than per course, because a block cut to close out one course is the block that starts the next one in a running bond. Waste on top is 5 percent for straight runs and 10 percent for curves, where every course needs its outside edge trimmed. Both rates are editable, and if your supplier sells by the pallet you will round up again at the counter anyway.

6. 6. Dig and fill the base trench

   The wall sits on compacted crusher run, not on soil and not on concrete. Allan Block's residential guidance is a trench 24 in wide by 6 in deep for walls at or above 4 ft and 18 by 4 below that; this tool seeds the width at the block depth plus 12 in, which lands in the same place, and both numbers are editable. Order it loose: 1.2 cubic yards loose compacts to about 1 cubic yard in the trench, which is why the base line on the ledger is bigger than the hole you dug.

7. 7. Build the drainage column, with the pipe and the fabric

   Twelve inches of clean angular stone, number 57 or similar, runs the full built height behind the wall with a 4 in perforated pipe sitting at its foot in the base, daylighted to the low end or to a solid outlet every 30 to 50 ft. Non woven filter fabric separates that column from the soil behind it so the fines cannot migrate in and blind it. Six inches of topsoil caps the column at the top so surface water sheds instead of pouring straight down it. Hydrostatic pressure is the single most common reason a wall leans, and this column is the whole defence against it.

8. 8. Glue the cap row

   Caps are not held by their own weight. A bead of exterior construction adhesive along the top course locks them down against frost heave, mower wheels and anyone who sits on the wall. A 10 oz cartridge of PL 500 runs 13.6 ft at a 3/8 in bead or 30.6 ft at 1/4 in, from Henkel's own technical data sheet, so the cartridge count comes off the linear feet of wall rather than off the block count. Both figures are editable in case your adhesive publishes different ones.

9. 9. Weigh the order before you plan the trip

   This is where retaining wall projects surprise people. The seeded 20 ft garden wall is 3,108 lb of block and cap plus 2.85 tons of stone, about 4.4 tons in total. A 40 ft wall at 3 ft is 13 tons. At a 1,500 lb half ton payload those are six and eighteen trips, so the honest answer is almost always delivery, and the delivery fee is a real line in the budget rather than an upsell.

10. 10. Price it as a ledger you can argue with

    Every price on this page is a seed you overwrite with your own supplier's number. The ledger totals from the rounded line costs, so what you read adds to the cent, and it prints a materials cost per linear foot beside the published installed range of roughly $40 to $120 per linear foot for a 2 to 4 ft wall. That comparison is the useful one: the gap between your materials figure and an installed quote is what the labour, the equipment and the contractor's risk are worth.

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.

Compacted gravel base or a concrete footing

A segmental wall wants a compacted gravel base, not concrete, and the reason is that it is a flexible structure. It is designed to settle and shift slightly with frost and moisture and to stay standing while it does, which a rigid footing prevents rather than helps. Mortared concrete block is the opposite: it is rigid, it cannot tolerate differential movement, and it wants a proper concrete footing below the frost line. If your wall is mortared CMU, the concrete block calculator owns that job including the footing helper, and this page is the wrong tool for it.

When half a course of burial is genuinely enough

The 1 in per foot rule is a wall rule, and a 12 in garden border that retains a few inches of mulch is not really a wall. On a decorative edge under about 12 in tall, burying half the first course to get it level and stable is normal practice and the tool's own rule reduces to exactly that anyway, because half a course beats 1 in per foot at that height. Above about a foot and a half, where the block is genuinely holding soil back, take the full rule and do not talk yourself down from it: the buried course is what stops the toe kicking out.

Setback, batter and the footprint you actually need

Lipped and pinned block leans back as it rises, typically 0.5 to 1 in per course. Over a 4 ft wall that is 6 to 8 in of lean, so the top of the wall sits most of a block depth behind the bottom, and the trench has to start far enough forward that the finished top lands where you want it. Draw the top line first and work down, especially where the wall runs beside a path, a fence or a property line, and remember the base trench is a foot wider than the block on top of it.

When the drainage column is skippable, and when it never is

A freestanding block seat wall or a border that retains nothing on either side does not need a drainage column, and paying for 12 in of clean stone behind it is money for nothing. Anything holding soil back needs one, without exception, including a wall that is only 18 in tall, because 18 in of saturated soil still generates hydrostatic pressure and that pressure is the number one reason walls lean. If you are unsure, look at whether one side is higher than the other after backfill. If it is, you are retaining, and the column goes in.

A slope or a load above the wall changes the question

A wall with flat ground behind it carries the weight of the soil it holds. A wall with a bank rising behind it, or a driveway, patio, pool deck or parking area on top of that soil, carries a surcharge as well, and surcharge loading is what pushes ordinary looking walls over. That is why this tool drops its design threshold from 4 ft to 3 ft when you tick the box: the honest answer above that is an engineer, not a bigger base. A pool, a retaining wall holding a driveway and anything a vehicle can drive on are all in that category.

Cap on or cap off, and what it does to the course count

The cap is not just a finish. It contributes its own height to what stands above grade, so it changes the arithmetic upstream of it. Take the seeded 20 ft wall: with a 3 in cap it is 6 courses and 126 blocks, and with the cap switched off it is 7 courses and 147 blocks, because the field now has to cover the exposure by itself. Decide the cap before you count anything, and if you are matching a wall that already exists, measure whether that one has caps rather than assuming.

Where the property line and the utilities actually are

A retaining wall is permanent, heavy and expensive to move, which makes it the worst possible structure to build a foot over a line. If the wall is anywhere near a boundary, get the line established before you dig rather than working off a fence that may itself be in the wrong place, and check the setback rules with the same phone call that asks about the permit. Utilities are the other half: 811 marks the public side, but the run from the meter to the house, the irrigation and the low voltage lighting are all yours and nobody is coming to mark them.

Common mistakes, and the fix

• × Building the first course on grade instead of below it.

  ✓ Bury the first course by the larger of 1 in per foot of wall height and half a course, on top of the compacted base. This is the cheapest structural thing you will do all week, it costs one extra course of block, and it is what stops the bottom of the wall walking forward under load and what stops rain undercutting the toe.

• × Skipping the drainage column, the pipe, or both, to save a few hundred dollars.

  ✓ Put in 12 in of clean angular stone the full height of the wall, with a 4 in perforated pipe at its foot daylighted every 30 to 50 ft, and non woven fabric between the stone and the soil. Water with nowhere to go is the number one reason walls lean, and the repair is rebuilding the wall. On the seeded 20 ft wall the whole drainage package is under $160 of the $765 order.

• × Treating segmental retaining wall block and mortared concrete block as interchangeable.

  ✓ They are different products with different math. Segmental block is dry stacked with a lip or a pin, no mortar, no cores to grout, its own setback, and geogrid rules above a certain height. Mortared CMU needs mortar, often grout and rebar, and a concrete footing below the frost line. This page owns the segmental wall; the concrete block calculator owns mortared CMU and its footing.

• × Forgetting that caps are a separate product on a separate pallet.

  ✓ Cap block is its own SKU with its own length, its own price and its own pallet, and it needs construction adhesive that most block counts never mention. On the seeded wall that is 21 caps and 2 cartridges, about $122 of a $765 order, and the caps also change the course count because they count toward the exposed height.

• × Trusting the catalog name for the block size.

  ✓ Put a tape on the block on the pallet. Two products both called a standard 16 in wall block can be 6 in or 8 in tall and 10 in or 12 in deep, and the depth drives the base trench width, the drainage column position and the setback. Type what you measured, not what the sign said.

• × Planning to haul four tons of wall in a half ton pickup.

  ✓ Check the weight line before you plan the trip. The seeded 20 ft garden wall is about 4.4 tons of material, which is six loads at a 1,500 lb payload, and a 40 ft wall at 3 ft is thirteen tons. Get it delivered, put the delivery fee in the budget, and have somewhere flat for the pallets to land near where the wall is going.

• × Building past 4 ft from a widget's block count because the numbers looked easy.

  ✓ Above 4 ft of exposed height, or 3 ft with a slope or a load above, this is an engineered structure. It needs geogrid layers sized to the soil and the surcharge, and in most jurisdictions a permit and a stamped design. This tool will still frame the budget for you and it will tell you plainly that the quantity list is not a design.

Material and unit specifics

Garden wall block, 12 x 4 x 8 in

The small tapered block sold for borders, raised beds and low steps, about 22 lb and roughly $3.50 each. Three of them cover a square foot of wall face. Its own manufacturers rate it for low walls only, commonly around 2 ft, and its shallow 8 in depth is why: there is very little block behind the face to resist the soil. Excellent for a bed edge, wrong for anything holding a real bank.

Standard SRW block, 16 x 6 x 10 in

The lipped or pinned block on most pallets, about 50 lb and roughly $7 each, at 1.5 blocks per square foot of face. This is what most residential retaining walls are built from and what most manufacturer literature is written about. It comes in a straight face and a corner or cap unit, and many lines include a half block so you can keep a running bond without cutting every course.

Large hollow SRW block, 18 x 8 x 12 in

The big hollow unit, about 75 lb, one block to the square foot of face, with open cores that get filled with the same clean stone as the drainage column. That core fill is real volume you have to order: on a 30 ft wall at 3 ft it adds about 25 cu ft, which is roughly a quarter of the stone on the ticket. The seed here is 0.25 cu ft a block and it is editable, because core sizes vary a lot between product lines. Measure or ask.

Crusher run against clean number 57, and never swapping them

The base course wants crusher run, also sold as road base or 21A: a graded mix with fines in it that compacts to a hard, stable platform. The drainage column wants the opposite, clean angular stone such as number 57 with the fines washed out, so water runs straight through it. Putting crusher run in the drainage column blinds it and defeats the whole point, and putting clean stone in the base gives you a platform that never compacts. Both are about 1.4 tons per cubic yard, and our gravel calculator covers the material selection and bulk pricing side.

Non woven geotextile, and why not the woven kind

The fabric between the drainage stone and the retained soil is there to separate, not to reinforce: it lets water pass and stops soil fines migrating into the stone and clogging it. That job wants a non woven needle punched fabric with real flow rate, not the woven black weed barrier sold in garden centres, which is a weed blocker and drains poorly. Rolls are commonly 3 by 50 ft, so 150 sq ft, and this page counts them off the column height plus a 2 ft wrap allowance.

Four inch perforated pipe, and daylighting it

The pipe sits at the foot of the drainage column, in the base, with its holes facing down so the water table it drains is at the bottom of the stone. It has to go somewhere: to a low point where it exits at the face, to a solid pipe run to a swale, or to a drywell. The usual guidance is an outlet every 30 to 50 ft, and a pipe with no outlet is just an expensive void. Sock covered pipe is convenient in clean stone; in dirtier backfill the sock is what eventually clogs.

PL 500 and the coverage figure this page uses

Cap adhesive is sold by the cartridge and used by the linear foot. Henkel's technical data sheet for PL 500 landscape block adhesive gives 13.6 ft per 10 oz cartridge at a 3/8 in bead and 30.6 ft at 1/4 in, which is the number seeded here and the number the cartridge count is worked from. Both are editable, and if you are running two beads on a wide cap, halve the coverage rather than doubling the wall length.

Geogrid, named here and deliberately not computed

Geogrid is a stiff polymer mesh laid in horizontal layers between courses and extending back into the retained soil, so the wall and a wedge of the soil behind it act as one mass. It is what makes a wall taller than a gravity wall can be. Its layer count, its embedment length and its vertical spacing are outputs of a calculation involving the soil type, the wall geometry and any surcharge on top, and they are wall-specific and product-specific. That is engineering, not a takeoff, so this tool names it and refuses to guess. Above 4 ft, or 3 ft with a load above, get a stamped design.

Pressure treated 6x6 timber and its deadmen

A nominal 6x6 measures 5.5 in and comes in 8 ft sticks weighing roughly 65 lb each when freshly treated. Timber walls are tied back into the bank with deadmen, timbers running perpendicular into the retained soil on alternating courses, trapped under the course above them and spiked home, which is why the top course never carries one. Ten to twelve inch landscape spikes fix the courses to each other and rebar pins hold the buried first course to the ground. All of it is trade practice with editable constants, and a timber wall still wants the same base, column, pipe and fabric a block wall does.

Reading your result

Read the built height before you read the block count. That single figure, the one the section drawing labels, tells you how much wall you are actually buying and how deep the trench has to be, and it is the number a face-area calculator never shows you. Then read the split at the bottom of the ledger: on a typical order between a quarter and a third of the money is base gravel, drainage stone, pipe, fabric and adhesive, and that share goes UP as the wall gets shorter, because a low wall is mostly its own foundation. The tons line is the reality check on logistics, since a wall that fits on a page is often thirteen tons in a driveway. The per linear foot figure is materials only and sits against a published installed range of roughly $40 to $120 per linear foot for walls of 2 to 4 ft, so the gap between the two is what you are being charged for labour, equipment and risk, and it is a useful thing to know before a quote arrives. If the design banner is showing, treat everything below it as a budget frame and nothing else: the quantities are real arithmetic on the geometry you typed, but a wall over the line is not defined by its geometry alone, and the missing piece is a stamped design rather than a bigger number.

Limitations

• This is an estimating tool, not engineering. Every structural figure on this page is manufacturer prescriptive guidance of the kind published in residential installation manuals, and it is yours to confirm with your local building department before you build.
• It does not compute geogrid, surcharge loading, global or internal stability, bearing capacity or soil parameters. Above 4 ft of exposed height, or 3 ft with a slope or a load above the wall, those are the things that actually decide whether the wall stands, and they come from a licensed engineer.
• Poured concrete cantilever walls are out of scope entirely. Those are a structural design problem with reinforcement schedules and stem thickness calculations, and engineering software rather than a takeoff calculator is the right tool for them.
• Mortared concrete block walls belong on the concrete block calculator, which handles mortar, grout, rebar and a concrete footing below the frost line. This page will get a mortared wall wrong in both directions: no mortar counted, and a gravel base where a footing belongs.
• Curved walls are handled as extra waste, not as geometry. A tight radius changes the effective run per course and may need a different block, so treat a curve as an approximation and check the manufacturer's minimum radius for the block you picked.
• All prices are editable seed values, not quotes. Block, cap and aggregate pricing varies enormously by region and by supplier, and delivery is usually a separate charge that is not in the ledger unless you add it.
• Steps, corners, columns, freestanding sections and wall ends that step down into grade are not counted as special units. If your wall has them, add their block by hand or measure them as their own runs.

Frequently asked questions

How many retaining wall blocks do I need per square foot?

It comes off the face size of the block, so it is one division: 144 divided by the block length times its height, both in inches. A 12 by 4 in garden block is 3 blocks per square foot of wall face, a 16 by 6 in standard block is 1.5, and an 18 by 8 in large block is exactly 1. Caps are counted separately by the linear foot, roughly one per foot for a 12 in cap. The catch is that square feet of face is the wrong starting point, because it measures what you can see: the wall is built taller than it stands, so count courses from the built height and not from the exposed height.

How deep should the base be for a retaining wall?

Allan Block's residential guidance is a compacted base 6 in deep in a trench 24 in wide for walls at or above 4 ft, and 4 in deep in an 18 in trench below that, always on undisturbed or properly compacted soil. On top of that the first course is buried by the larger of 1 in per foot of exposed height and half a course, so a 3 ft wall sits in a trench about 9 in below the finished grade in front of it. This tool seeds the trench at the block depth plus 12 in and every figure is editable. Confirm the numbers locally, since frost depth and soil bearing are local questions.

Do I really need drainage gravel and a pipe behind the wall?

If the wall is holding soil back, yes, and it is the least optional thing on the list. Put 12 in of clean angular stone up the full built height, a 4 in perforated pipe at its foot daylighted every 30 to 50 ft, non woven fabric between the stone and the soil, and 6 in of topsoil capping the column. Water building up behind a wall is the number one reason walls lean and fail, and it is a rebuild rather than a repair. On the 20 ft wall this page opens with, the whole drainage package is 1.81 tons of stone, 2 sticks of pipe and a roll of fabric, about $158 of a $765 order. The exception is a wall that retains nothing, like a freestanding seat wall.

How tall can I build a retaining wall without an engineer?

Most manufacturers cap an unreinforced gravity wall somewhere near 3 ft, and 4 ft of exposed height is the common threshold at which a jurisdiction wants a permit and a stamped design. Any slope, driveway, patio, pool deck or parking area above the wall is a surcharge, and it drops that threshold to about 3 ft because the loading changes completely. This tool switches its own tone at those lines: it warns, it relabels the ledger as a budget frame rather than a design, and it names geogrid as something it will not compute. Treat all of that as guidance and confirm with your building department, because the exact numbers vary by jurisdiction.

What does a retaining wall cost per linear foot?

For materials only, at the editable seed prices on this page, a 20 ft garden wall at 2 ft works out at $38.27 a linear foot and a 40 ft standard block wall at 3 ft at $52.20. Published installed costs run roughly $40 to $120 a linear foot for walls in the 2 to 4 ft range, which is context rather than a quote: the spread is labour, equipment, excavation, disposal and the contractor's risk, and it moves a long way with access and soil. The useful exercise is to price your own materials here, then read an installed quote as materials plus everything else, and ask what the everything else covers.

Why is the block count higher than the wall area suggests?

Three reasons, and the tool prints all three. The first course is buried, so the wall is built taller than it stands: 27 in of block to show 24 in. The cap counts toward the exposed height, so switching it off adds a course rather than just removing a shopping list line. And waste is 5 percent on a straight run and 10 percent on a curve. On a low wall the cap height happens to offset the burial and the counts coincide, but above roughly 3 ft of exposure the 1 in per foot rule outruns a 3 in cap and the wall gains a whole course a face-area count never sees.

Can I build a retaining wall out of timber instead of block?

Yes, and this page has a timber mode for pressure treated 6x6 timbers, but the burial rule is different and that difference matters. You cannot backfill to the middle of a 5.5 in timber face, so the buried part of a timber wall is always a whole course, at least one, and the courses above grade are whole courses too. A 24 ft wall asked for 2 ft of exposure therefore finishes at 27.5 in on 6 courses, and needs 22 timbers once the deadmen are counted, 42 spikes and 6 rebar pins. Timber walls are also tied back into the bank with deadmen on alternating courses, never on the top course, because a deadman has to be trapped under the course above it. Expect roughly 20 to 30 years of service against many decades for block.

What is geogrid, and why will this calculator not size it?

Geogrid is a stiff polymer mesh laid between courses and extending back into the retained soil, so the wall and a wedge of soil behind it act as a single mass. It is how walls get taller than gravity alone allows. Sizing it means knowing the soil's friction angle and cohesion, the wall geometry, the water conditions and any surcharge, then checking sliding, overturning, bearing and global stability. That is engineering, and getting it wrong looks fine for a couple of winters and then does not. This tool names geogrid as a layer it deliberately leaves blank and routes you to a stamped design instead of guessing.