Grass Seed Calculator - Pounds, Bags, Coverage & Cost

How to use it

1. Measure the lawn in pieces. Break the yard into rectangles, circles and triangles against the fence, the drive and the beds rather than fighting one odd shape, and add a row for each. Feet and inches get their own boxes, so 12 ft 7 in never quietly becomes 12.7 ft. If you already know a square footage, switch that row to Known area and type it in.
2. Take off what is not lawn. The house pad, the driveway, the patio, the shed, the planting beds. These come off the total as their own rows, and on a typical lot the difference between the parcel and the lawn is a third of the order. The takeoff table shows every piece with its pounds beside it, deductions included as negatives, and the rows add up to the headline.
3. Say what the job is. New lawn means bare soil: tilled ground, a strip after construction, a full renovation. Overseeding means live grass you are thickening. The rate halves between them, and the result panel shows both so you can see what the other choice would cost.
4. Set the rate. Pick your grass and the tool loads the seeding rate published by Cornell, Penn State or NC State for it, with the source band printed beside the slider so you can move it inside the range that extension actually supports. If you are holding a coated retail bag, switch to bag label mode instead and type the coverage figure off the bag, because a coated product is part coating by weight and species-rate math over-buys it.
5. Read the analysis label. Every legal bag prints percent purity and percent germination. Type them in and the tool converts the chart weight into the weight to actually buy. The button beside the fields loads the published minimum standard for your species where Penn State publishes one, so you can see whether the bag in your hand clears it.
6. Pick the bag size and price. Bag size decides waste more than anything else on the page: the same 53.9 lb order is two 50 lb bags with 46 lb spare, or three 20 lb bags with 6 lb spare. Prices are yours to edit and default to plausible shelf figures, not quotes.
7. Add the extras and read the ledger. Starter fertilizer by its own coverage, straw or peat cover for a new lawn only, and a planning total with the cost per square foot so you can hold it against sod.

At a glance

• 5,000 sq ft, new tall fescue at 8 lb per 1,000: 40 lb on the chart, 49.5 lb to buy at a 95/85 label, one 50 lb bag with 0.5 lb spare
• The same lawn overseeded: 20 lb on the chart, 24.8 lb to buy: half the seed, half the bill
• 2,500 sq ft of bluegrass at 2 lb, weak label (90/75): 5 lb on the chart, 7.4 lb to buy, and one 10 lb bag beats two 7 lb bags
• A quarter acre overseeded with tall fescue: 53.9 lb to buy: three 20 lb bags leave 6.1 lb spare, two 50 lb bags leave 46.1 lb
• One 50 lb bag of tall fescue seed: 6,250 sq ft of new lawn as raw weight, 5,047 sq ft of it viable at a 95/85 label
• Seed against sod, materials only: About $0.03 to $0.08 a square foot against $0.30 to $0.85, and a season of waiting

How the math works

Every length is held in inches, which is why feet and inches get separate boxes. A rectangle is length times width, a circle is pi times the diameter squared over four, a triangle is base times height over two, and a known area goes straight through. Sections add, deductions subtract, and the net is floored at zero. Seeding rates are quoted per 1,000 square feet, so the net area divides by 1,000 and multiplies by the rate to give the chart weight, and dividing by 43,560 gives acres for the per-acre line. The purchase weight is that chart weight divided by pure live seed, where pure live seed is purity times germination straight off the bag: 0.95 times 0.85 is 0.8075, so a 40 lb chart answer becomes 49.5 lb to buy, and Cornell's roughly 20 percent allowance falls out of the arithmetic as an exact 23.8 percent rather than being asserted as a rule of thumb. Bags are the purchase weight over the bag size, rounded up, with the leftover printed. Bag label mode skips the pure live seed step entirely and works backwards from the coverage on the bag instead, because a coated product's stated coverage already carries its coating and its seed quality, and applying the label math again would buy the same allowance twice. Starter fertilizer and cover bales each round up on their own coverage figures. The per section pound rows are apportioned against the printed purchase weight using largest remainder, so the column you read adds up to the figure it sits under, deductions included as negative rows, rather than each row being rounded on its own and hoped over.

1. 1. Net the lawn, not the lot

   Add every measured section, subtract the house pad, the drive, the patio and the beds, and floor the result at zero. A 50 by 40 front and a 75 by 44 back measure 5,300 sq ft; take off a 20 by 15 driveway and you are seeding 5,000. Every row keeps its own dimension line so you can check the tape against the plan, and a deduction shows in the takeoff as a negative row in both square feet and pounds.

2. 2. Pick the rate from the species, not from the bag front

   Rates are pounds per 1,000 square feet of VIABLE seed on bare soil. Cornell puts Kentucky bluegrass at 1 to 3 and turf-type tall fescue at 6 to 8; Penn State agrees on tall fescue and puts perennial ryegrass at 4 to 5 and a pure fine fescue stand at 4 to 5; NC State's Table 9-4 covers the warm season grasses, seeding bermudagrass and zoysia at 1 to 2, centipede at 0.25 to 0.5 and bahiagrass at 5. Each preset here sits inside those published bands and prints its source, and the slider stays inside the range so a disputed number is an adjustment rather than a bug.

3. 3. Halve it for overseeding

   Overseeding puts seed into a living lawn that is already holding the ground, so the standard homeowner allowance is half the new-lawn rate. Tall fescue at 8 becomes 4, bluegrass at 2 becomes 1. Cornell's sports field table runs far higher, 10 to 15 lb of ryegrass per 1,000 sq ft, but that is a football field being reseeded weekly under cleats, not a back yard. Both answers appear on the result panel so the halving is visible rather than trusted.

4. 4. Correct for what is actually in the bag

   Pure live seed is purity times germination, both printed on the analysis label by law. At 95 percent pure and 85 percent germination the factor is 0.8075, so the purchase weight is the chart weight divided by 0.8075, about 24 percent more. Penn State publishes suggested minimum standards for the common species (bluegrass 90 and 80, ryegrass 95 and 85, tall fescue and fine fescue 95 and 80) and the tool warns when the bag in front of you is under them, because a cheaper bag that needs a fifth more of it is usually the more expensive bag.

5. 5. Round to bags, and count the leftover

   Bags are the purchase weight over the bag size, rounded up. This is where the money leaks: 53.9 lb is two 50 lb bags with 46.1 lb left on the shelf of your garage, or three 20 lb bags with 6.1 lb. The tool prints the spare weight next to the bag count so the bag size stops being an afterthought. Leftover seed keeps for next year's repairs if it stays sealed, cool and dry, losing roughly a tenth of its germination a year.

6. 6. Add the seedbed extras

   Starter fertilizer covers about 5,000 sq ft a bag, so most lawns take one or two. Straw covers roughly 750 sq ft a bale and is a new-lawn line only, since an overseeded lawn already has cover standing on it. Peat moss at a quarter inch is the tidier alternative at roughly 350 sq ft per compressed 3.8 cu ft bale. All three coverage figures are editable because bag sizes vary by brand.

7. 7. Total it as a plan, not a quote

   Seed bags times price, plus fertilizer, plus cover, with the cost per square foot printed underneath. On the default job that is $159.99 of seed over 5,000 sq ft, about $0.032 a square foot, and $252.83 all in at about $0.051. Those are editable defaults picked to be plausible on a US shelf, not prices anyone quoted you, and they are what makes the seed against sod comparison at the bottom of this page arithmetic instead of an opinion.

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.

Overseed or start over

The working rule is the half test: stand back and judge what fraction of the area is still grass you want. More than about half means overseed at the half rate and keep the difference. Less than half, or a lawn that is mostly crabgrass, nutsedge or bare compacted soil, means renovation at the full new-lawn rate, because seed dropped into a weed stand loses the race for light and water before it has a second leaf. Renovating properly also means killing what is there and getting seed into soil contact, which is a weekend of work, not a bag.

When to seed, honestly

For cool season grasses, tall fescue, bluegrass, ryegrass and fine fescue, the best weeks of the year are mid August through late September. Soil is still warm enough to germinate fast, air is cooling, and the seedlings get autumn, winter and spring to root before their first summer. Spring is second best and genuinely worse: crabgrass germinates alongside you, pre-emergent herbicide cannot be used, and the seedlings meet July with a three month root system. Warm season grasses invert this, wanting late spring into summer once soil is reliably above 65 F, which is why NC State's table seeds bermuda and zoysia April through July. Seeding outside the window is not a rate problem and cannot be fixed with more seed.

More seed is not better

NC State says it in one line: do not assume more seed is better. Overcrowded seedlings compete with each other for light, water and nutrients, damp off in humid weather, and thin themselves out to roughly the stand you would have got at the right rate, having cost you double. The one legitimate reason to go to the top of the published range is bare soil in a short window with imperfect coverage, which is exactly why the tall fescue default here sits at 8 rather than 6.

Coated seed or raw seed

Many retail bags are coated to hold moisture and take fertilizer or fungicide with them, and the coating is real weight you are buying. That is why a coated bag's own coverage figure, not its weight, is the number to compare, and why this page has a bag label mode. NC State makes the same point from the other side for bermudagrass: if the seed is coated, the seeding rate may need to be doubled. Using a species rate on a coated product over-buys it; using a coated bag's coverage on raw seed under-buys.

Starter fertilizer and the phosphorus rule

Starter fertilizer is high in phosphorus because phosphorus drives root development, and new seedlings need roots more than they need top growth. A number of states restrict phosphorus lawn fertilizer to protect waterways, and the usual carve-out is exactly this case: establishing a new lawn, or a soil test showing a deficiency. Check your state's rule before buying, and take the soil test anyway, because it also tells you the lime question that no calculator can answer for you.

Straw, peat, or nothing

Cover keeps the seedbed from drying between waterings, which is the single most common reason a new lawn fails. Straw at about 750 sq ft a bale is the cheap answer, and clean straw is the point: hay carries weed seed. Peat at a quarter inch is tidier and does not blow, at roughly 350 sq ft per compressed bale, and costs more. Nothing at all is a real option if you can water lightly two or three times a day, and a bad option if you cannot.

Common mistakes, and the fix

• × Using the new-lawn rate to overseed, which buys about double and chokes the seedlings that do come up.

  ✓ Set the project to Overseeding. The rate halves, and the result panel keeps the new-lawn answer beside it so you can see exactly what the difference is worth.

• × Reading the weight on a coated bag as if it were all seed, then applying a species rate on top of it.

  ✓ Switch to bag label mode and type the coverage figure the bag prints for new lawn and for overseeding. A coated product's coverage already accounts for the coating and the seed quality.

• × Using the bag's new-lawn coverage number for an overseeding job, or the overseed number for bare soil.

  ✓ Retail bags print both, usually as a big number and a small one. The tool asks for both and uses the one that matches the job, with the other shown as the contrast.

• × Measuring the whole lot instead of the lawn, so the house, the drive and the beds all get seeded on paper.

  ✓ Enter them as deductions. They appear in the takeoff as negative rows in both square feet and pounds, so you can see what came off and check it.

• × Ignoring purity and germination because the numbers are in small print on the back of the bag.

  ✓ Type them into the analysis label panel. It is the difference between 40 lb and 49.5 lb on a 5,000 sq ft lawn, and the fields default to a normal good label so you can see the effect before you find the tag.

• × Seeding cool season grass in May because that is when the garden centre display goes up.

  ✓ Wait for mid August through late September if you possibly can. Spring seeding competes with crabgrass, rules out pre-emergent herbicide, and sends young grass into summer with three months of root.

Material and unit specifics

The analysis label

Every legal US bag carries a tag listing each species and variety, its percent purity by weight, its percent germination, other crop seed, weed seed, undesirable grass seed, inert matter and the date the germination test was run. Purity times germination is pure live seed, the only part you are really buying. Watch the test date too: germination is measured, not guaranteed forever, and a tag tested eighteen months ago is describing a bag that has aged since.

Pure live seed in one line

Purity times germination. Cornell's worked example is a bluegrass blend at 95 percent pure and 85 percent germination, which it reports as 81 percent pure live seed and roughly 20 percent more to buy. Carried out exactly, 1 divided by 0.8075 is 1.238, so it is nearer 24 percent, and this tool uses the exact division rather than the rounded allowance. Penn State works the same sum the other direction: divide 100 by the PLS percentage to get the pounds needed per pound specified, so an 85 by 72 bag needs 1.6 lb for every 1 lb the plan calls for.

Blends, mixtures and what the percentages mean

A blend is several varieties of one species; a mixture is several species. The percentages on the label are BY WEIGHT, and weight is not seed count. Cornell's example is exact: a mixture that is 70 percent perennial ryegrass and 30 percent Kentucky bluegrass by weight comes out roughly 50:50 by seed count, because ryegrass seed is about six times heavier. Read a mixture label as a weight recipe and expect the fine-seeded species to be a larger share of the plants than of the bag.

Seeds per pound, and why rates differ

Cornell publishes the two that matter: about 1.5 million seeds in a pound of Kentucky bluegrass and about 250,000 in a pound of perennial ryegrass. So bluegrass at 2 lb per 1,000 sq ft puts about 21 seeds on every square inch while ryegrass at 5 lb, two and a half times the weight, puts about 9. A ryegrass seed is roughly six times the weight of a bluegrass seed and makes a far bigger seedling, so it needs fewer of them. The pound is a packaging unit, not an agronomic one. Seed counts for the other species on this page are approximate and labelled as such.

Coated seed

A coating carries moisture-holding material and often fertilizer or fungicide, and it can be a large fraction of the bag by weight. That makes coverage, not weight, the comparable number between a coated bag and a raw one. NC State's guidance for coated bermudagrass is that the rate may need doubling, which is the same fact seen from the seed's side.

Spreader settings

This page outputs pounds and bags, never dial numbers. Spreader settings are specific to the brand, the model, the seed size and your walking speed, so a number copied from a calculator is a guess dressed as a fact. Set the dial low, weigh out the seed for a measured strip, spread half of it in one direction and half at right angles, and adjust from what actually landed.

Reading your result

The big figure is the weight to buy, not the weight the chart calls for, and the line under it tells you which is which. If pure live seed is on, the purchase weight is always higher than the chart weight, and the gap IS the label: at 95 and 85 it is about 24 percent more, at 90 and 75 it is nearly half again. The bag line is the practical answer, and the spare weight beside it is the number to check before you commit to a bag size, because on a 50 lb order that spare can be a whole bag. The contrast figure shows the same lawn done the other way, new against overseeded, so you can see what the project choice is worth before the rate is settled. The takeoff table adds up to the headline whenever there is lawn left to seed, deductions included as negative rows, so if the total looks wrong the row that is wrong is visible. Take off more than you measured and the total floors at zero rather than printing a negative lawn, and the panel says so instead of quoting a weight. Treat the cost ledger as a plan you edit rather than a quote: the prices are plausible shelf figures, and the per square foot line at the bottom is what makes the comparison against sod real.

Limitations

• Seeding rates are agronomic guidance from Cornell, Penn State and NC State, not a recommendation for your specific site. Soil, shade, slope, irrigation and traffic all move the right answer, and a local extension office will beat any published table for your county.
• The tool sizes an order. It cannot tell you whether the seed will take, which depends on seedbed preparation, soil contact, watering and the calendar far more than on the pounds.
• Species presets cover the ten grasses commonly seeded on US lawns. Bentgrass, rough bluegrass, annual ryegrass and native prairie mixes are outside the presets, though the rate box takes any number you can source.
• Seed counts per pound are exact only for Kentucky bluegrass and perennial ryegrass, which Cornell publishes. The rest are approximate industry figures used for the density picture and marked as approximate.
• Prices are editable placeholders chosen to be plausible on a US shelf in 2026, not quotes, and seed prices move with the season and the variety.
• Above about five acres this stops being a bag-count problem and becomes a per-acre bulk purchase with different equipment. The tool says so and gives the per-acre figure, but a seed dealer is the right next call.

Frequently asked questions

How much grass seed do I need for 1,000 square feet?

It depends on the species, and the spread is wide. On bare soil, per 1,000 sq ft: Kentucky bluegrass 1 to 3 lb, a bluegrass and ryegrass mix 3 to 5 lb, perennial ryegrass 4 to 6 lb, fine fescue 4 to 5 lb, turf-type tall fescue 6 to 8 lb, bermudagrass and zoysia 1 to 2 lb, bahiagrass about 5 lb, and centipedegrass just 0.25 to 0.5 lb. Overseeding an existing lawn takes about half of those. Those are rates of VIABLE seed, so a bag at 95 percent purity and 85 percent germination means buying about 24 percent more than the figure quoted. The printable chart further down this page carries every species with the per acre and per bag figures beside it.

How much does a 50 lb bag of grass seed cover?

As raw product weight, a 50 lb bag covers 6,250 sq ft of new tall fescue lawn at 8 lb per 1,000 sq ft, or 25,000 sq ft of new Kentucky bluegrass at 2 lb. Those are the figures a bag or a chart will quote you and they ignore seed quality. Apply a normal 95 percent purity and 85 percent germination label, which is 80.75 percent pure live seed, and the same bag really covers 5,047 sq ft of tall fescue and 20,188 sq ft of bluegrass. Overseeding doubles both, since the rate halves. The chart on this page prints the raw figure and the tool prints the adjusted one, so you can see the difference rather than pick between two numbers.

How much grass seed do I need per acre?

Multiply the rate per 1,000 sq ft by 43.56, since an acre is 43,560 sq ft. New tall fescue at 8 lb per 1,000 is 348.5 lb an acre; Kentucky bluegrass at 2 lb is 87.1 lb; perennial ryegrass at 5 lb is 217.8 lb. Those are chart weights. On a typical 95/85 label the tall fescue acre becomes 431.6 lb to buy, which is 9 fifty-pound bags rather than the 7 the chart weight suggests. At acre scale, ask a seed dealer about bulk sacks: the price per pound falls sharply above about 100 lb, and a tow-behind broadcast spreader stops being optional.

Is grass seed or sod cheaper?

Seed is roughly 10 to 20 times cheaper in materials: about $0.03 to $0.08 a square foot against $0.30 to $0.85 for sod, so on an 8,000 sq ft lawn that is a few hundred dollars against several thousand. What the saving costs is a season. Seed needs light watering two or three times a day for two to three weeks to germinate, gets a weed flush while it is thin, cannot take traffic for a couple of months, and usually wants overseeding the following year before it looks like a lawn. Sod is a finished lawn the day it goes down and holds a slope while it roots, where seed washes off in the first storm. Some grasses, St. Augustine among them, are not sold as seed at all. Our sod calculator sizes the pallets if you go the other way.

When is the best time to plant grass seed?

For cool season grasses, tall fescue, bluegrass, ryegrass and fine fescue, mid August through late September is the best window of the year across most of the US: warm soil for fast germination, cooling air, and three seasons of root growth before the first summer. NC State's table puts it at August 15 to September 1 in the mountains, September 1 to 15 in the piedmont and September 15 to October 15 on the coast, which is the same window sliding later as you go south. Spring is a real second choice but a worse one, because crabgrass germinates alongside the seed and pre-emergent herbicide is off the table. Warm season grasses are the other way round: NC State seeds bermudagrass and zoysia April through July and centipede March through July, once soil is reliably above 65 F.