Grass Seed Calculator

How to use this calculator

1. Say whether it is a new lawn or an overseed. This is the first question because it roughly halves the answer. Establishing grass on bare soil takes roughly twice the seed of thickening turf that is already there, which is why it is the first control on the page rather than a footnote.
2. Put in the grass area, not the lot size. Subtract the house, the drive, the beds and the patio. If you have never measured it, switch to Measure it for me and enter the front, back and side patches separately; a walking stride is close enough to three feet that pacing lands inside the seeding-rate range anyway.
3. Pick the actual grass. The rate is per species and the spread is enormous. Centipedegrass goes down at a quarter of a pound per 1,000 square feet and bahiagrass at ten. Sowing one at the other's rate is not a rounding error.
4. Open the seed tag panel and read the bag. Purity and germination are printed on every bag by law. Type them in. This is the step that changes the number of bags in your trolley, and it is the reason this page exists.
5. Set the bag size you are buying. The answer comes back as bags and leftover pounds, not as a decimal weight you then have to divide in the aisle.
6. Take it with you. Copy the result as text, share the link (it carries every input), or download the seeding plan PDF for whoever is standing at the counter.

Why this grass seed calculator is different

I sat down and actually used the five calculators ranking for this search, typing the same lawn into each one. Some of them are good. The gaps they share are specific:

• Not one of them asks what is on the bag. Across all five pages there is no mention of pure live seed, purity or germination anywhere. State seed law makes every bag carry a tag printing what share of it is the seed you wanted and what share of that will sprout, and extension seeding rates are written in pure live seed. Every calculator on page one quietly assumes your bag is perfect. None is.
• Not one of them cites a source. No extension service, no university, no USDA, on any of the five. That matters because they disagree with each other badly: Kentucky bluegrass is published as 2 to 3 pounds per 1,000 square feet on one and a flat 4 on three others; tall fescue as 6 to 10 on one and a flat 10 on three. Every rate here is linked to the publication it came from, in the table below.
• They give you a number where the honest answer is a range. Published tall fescue rates run from 4 pounds to 10 across the states, and the spread is real: seedbed, irrigation and season all move it. This tool shows the whole published band next to the working figure and tells you which end you are at.
• Bags are an afterthought. Three of the four questions Google shows under this search are bag questions. Exactly one of the five calculators does bag math, and it is folded inside a collapsed panel most visitors never open. Here it is on the result card.
• Timing and technique are split between two of them. One page tells you when to sow and nothing about doing it; another covers spreader calibration and slopes and never mentions a date. Both are on this page, per species.
• Coated seed stops being a trap. A coating is inert weight that shows up in the purity line, and Wisconsin notes it can pull purity down to 66%. On an 8,000 square foot sun and shade mix with an 85 / 80 tag, that is 68% pure live seed: 28 pounds of live seed on the ground means buying 41.2 pounds, three bags instead of two.
• Nothing here is gated, and nothing here is printed for you elsewhere. None of the five will hand you a printable seeding plan, and none of them keeps the number in view on a phone while you change the inputs. Of the two that offer an embed at all, one wants your email address first. This one is a copy-paste iframe, free, with no tracking attached.

How it works (the math behind the numbers)

Two steps. The first is the one every calculator does. The second is the one that decides how many bags you buy.

live_seed_lb = area_sqft / 1000 x rate_lb_per_1000

PLS          = purity% x germination% / 100
bulk_lb      = live_seed_lb / PLS            <- the pounds you actually buy

bags         = ceil(bulk_lb / bag_lb)
left_over    = bags x bag_lb - bulk_lb
bag_covers   = bag_lb x PLS x 1000 / rate

The rate is per species and per purpose, and it is a pure live seed figure. Work an example. A 5,000 square foot new lawn of turf-type tall fescue at the published 7 pounds per 1,000 square feet needs 35 pounds of living seed on the ground. A good tall fescue tag reads 95% purity and 85% germination, which is 80.8% pure live seed. So the bag you carry home has to weigh 43.3 pounds, not 35. That is 8.3 pounds of difference on an ordinary suburban lawn, and it is entirely invisible unless somebody asks for the tag.

The pure live seed formula is the USDA's, stated in the Natural Resources Conservation Service technical note as purity times germination divided by one hundred, with bulk seed as the recommended rate divided by that fraction. The calculator reproduces the NRCS's own worked example and the four species percentages published in UMass Extension's seed-label table exactly, and those comparisons run as assertions on every build, so the math on this page cannot drift away from the agencies it came from.

Leave the tag blank and pure live seed is treated as 100%, so the published rate passes through untouched. A missing tag should never silently inflate your order.

Published seeding rates by species

Pounds per 1,000 square feet, in pure live seed. These are the figures the calculator uses, rendered from the same data file the build gate checks.

Each grass name links to the extension publication the rate came from. Overseeding rates follow Kansas State's half-of-establishment rule except where a state publishes a rate specifically for overseeding, which is why the two ryegrass rows read higher than the rule would predict.

Three worked examples

8,000 sq ft of tired tall fescue, overseeding in September

The standard autumn job across the transition zone. Overseeding runs at half the establishment rate, so 3.5 pounds per 1,000 square feet rather than 7, and 8,000 square feet needs 28 pounds. In 20 pound bags that is two bags with 12 pounds spare. The published range for this lawn is 24 to 32 pounds, so if the turf is merely thinning go to the bottom of it and if there are genuine bare patches go to the top. Do this before you put the mower away for the season, not after, because the seedlings want cutting once before frost.

6,000 sq ft of new Kentucky bluegrass, with the tag read properly

Bluegrass goes down light: 2.5 pounds per 1,000 square feet, so 15 pounds of live seed for 6,000 square feet. Then read the bag. A typical bluegrass tag is 90% purity and 75% germination, which is only 67.5% pure live seed and the weakest of the common lawn grasses. Fifteen pounds of living seed means buying 22.2 pounds, an extra 7.2 pounds, which turns one 20 pound bag into two. Every calculator that skips the tag would have sent you home a bag short on the cheapest part of the job.

An acre of bermudagrass from bare ground

An acre is 43,560 square feet. Seeded bermuda goes in at 1.5 pounds per 1,000 square feet, so 65.3 pounds, or two 50 pound bags. The published range across the southern states is 43.6 to 87.1 pounds for this same acre, which tells you how much judgement sits in that number: go heavy on a rough, un-irrigated seedbed and light where you can water twice a day. Sow it in May or June and not after the first of July, because a later sowing has no time to root before cold weather. An acre also means a hose that actually reaches the far corner, which is a bigger practical constraint on this job than the seed is.

What changes how much seed you actually need

• The tag, more than anything else on this page. Purdue's buying guide sets the standard at 90% purity or better and 85% germination or better, and a bag below that is not a bargain, it is less seed. Wisconsin's rule of thumb is that if pure live seed falls under 85% you should be adjusting the rate rather than ignoring it.
• A bag of “seed and mulch” is not a bag of seed. Seed-and-mulch and patch-and-repair products are mostly mulch and starter fertiliser by weight. A five pound bag of a centipede seed-and-mulch product is applied at around two and a half pounds of product per 1,000 square feet against a quarter to a half pound of actual centipede seed, and patch products run higher still. Do not put those bag weights into a seeding rate. If you are buying one, follow the coverage printed on the bag and ignore this calculator's pound figure.
• Compare the bag's own coverage figure against the table below. Divide the bag weight by the square feet it claims to cover, times a thousand, and you have the rate its maker is assuming. Coated and fertiliser-bulked products land well above the extension band, which is expected. Several mainstream cool-season mixes land below it, which is not, and a coating cannot explain a low number because a coating only adds weight. If the bag's implied rate is thin, use the override field and sow at the published rate instead.
• Coated seed is heavier per living seed. The coating is inert weight that lands in the purity line on the tag. NC State puts it plainly for bermudagrass: if the seed is coated, the seeding rate may need to be doubled. Enter the tag figures and the calculator does that for you.
• Spring seedings need more than autumn ones. Rutgers says it outright: less favourable growing conditions mean a heavier rate for every turfgrass type. Missouri publishes separate spring and autumn columns, and the spring figure is roughly half again as high.
• Sowing heavier does not give you a thicker lawn. It gives you seedlings competing with each other for water and light, and a stand that thins out by its second summer. Extension rates target roughly one to two thousand seedlings per 1,000 square feet for a reason. North Carolina State puts it in four words: do not assume more is better.
• Watering decides the outcome, not the weight of seed. If the seedbed dries out once after the seed has swelled and before roots form, those seedlings are dead. Light watering two or three times a day for two to three weeks is the entire job.
• Spread it in two passes at right angles. Half the seed walking one direction, half across it. A single pass leaves stripes you will be looking at until the following season, and on very fine seed like centipede, Clemson suggests mixing it with corn meal just to get it spreading evenly.
• Mow before you overseed, and cut the edges first. Seed has to reach soil. Scalping the lawn short and clearing the clippings is what gets it there, and a string trimmer along the fence lines and the mailbox post stops those strips from being the thin bits next spring.

Frequently asked questions

How do you calculate how much grass seed you need?

Divide the lawn area in square feet by 1,000, then multiply by the seeding rate for your grass in pounds per 1,000 square feet. That gives the pure live seed you need on the ground. Then divide by the pure live seed percentage from the bag's tag, which is purity times germination divided by one hundred, to get the bulk pounds you have to buy. The second step is the one almost everybody skips.

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

It depends entirely on the grass and the job. For a new tall fescue lawn at 7 pounds per 1,000 square feet, a 50 pound bag covers about 7,143 square feet. For bermudagrass at 1.5 pounds it covers more than four times that; for bahiagrass at 7.5 pounds it covers slightly less. And if the tag is below 100% pure live seed, which every real bag is, the bag covers proportionally less than those figures.

How many pounds of grass seed per 1,000 sq ft for overseeding?

Roughly half the new-lawn rate, which Kansas State states as the general rule. For tall fescue that is 3 to 4 pounds against 6 to 8 for a new lawn; for Kentucky bluegrass, 1 to 1.5. Perennial ryegrass is the exception, because Penn State publishes a renovation rate of 4 to 6 pounds that is higher than its establishment rate: ryegrass is what you reach for when you need cover quickly.

How many square feet will 20 pounds of grass seed cover?

On tall fescue, about 2,857 square feet for a new lawn and 5,714 square feet overseeding, because the overseeding rate is half. That single bag covers very different amounts of ground depending on which of those two jobs you are doing, which is why the calculator asks first.

How many 50 lb bags of grass seed per acre?

For a new tall fescue lawn, an acre is 43,560 square feet and needs 304.9 pounds, which is seven 50 pound bags. Overseeding the same acre takes half that. Warm-season grasses need far less: seeded bermudagrass covers an acre on two bags.

When is the best time to plant grass seed?

For cool-season grasses, late August to mid-September in most of the country. Purdue puts the Midwest window at August 15 to September 15, Rutgers runs it into early October in New Jersey, and North Carolina State stretches it to mid-October on the coast. Seedlings then get two cool growing seasons before they meet a summer. Spring is the fallback, not the plan. Warm-season grasses are the opposite: May and June, once the soil has genuinely warmed, and Arkansas is blunt that bermuda should not go in after July 1.

What is pure live seed, and do I really have to care?

Pure live seed is the share of the bag that is both the seed you wanted and capable of sprouting. A 95 / 85 tall fescue tag is 80.75% pure live seed; a 90 / 75 bluegrass tag is 67.5%. On a bag of sun and shade mixture the per-component purity lines routinely read in the twenties, because purity is a share of the whole bag. You care because it is the difference between two bags and three, and because it is the only honest way to compare a cheap bag against an expensive one.

Related tools

• Sod Calculator — if you want a lawn this weekend rather than in six weeks, price the same square footage in pallets of sod.
• Topsoil Calculator — how many yards it takes to level a bumpy lawn before you seed it, and what that load weighs.
• Raised Garden Bed Soil Calculator — for the beds you carved out of the lawn area you just subtracted.
• All free tools by Jake — the full set of calculators and reference charts.

Methodology and sources

Seeding rates are the published figures from land-grant university extension services, in pounds of pure live seed per 1,000 square feet, with each species linked to the publication it came from in the table above. Where states disagree, the range shown is the full published spread and the working figure is its midpoint. The pure live seed arithmetic is the USDA's, and the calculator's output is asserted against the NRCS's own worked example and UMass Extension's published per-species percentages on every build, alongside worked fixtures and a set of assertions that pin the numbers quoted in this article to the calculator above it.

• Penn State Extension — Lawn Establishment (Table 1 seeding rates: turf-type tall fescue 6-8, Kentucky bluegrass 2-3, fine fescues 4-5, perennial ryegrass 4-5 lb/1,000 sq ft; plus the overseeding/renovation row for perennial ryegrass at 4-6; late-summer seeding window)
• Penn State Extension — Turfgrass Seed and Seed Mixtures (mixture rates: bluegrass/fine fescue/perennial ryegrass blends at 3-4 lb/1,000 sq ft)
• Penn State Extension — The Cool-Season Turfgrasses (Table 1, optimum soil temperatures for germination by species)
• K-State Research and Extension, Johnson County — Seeding a Fall Lawn (the overseeding rule: "applied at half the seeding rate that is used for new lawns on bare soil. For tall fescue, the normal rate is 6 to 8 pounds per 1000 square feet, so the overseeding rate is 3 to 4 pounds")
• USDA NRCS Technical Note PLANT MATERIALS-03 — Pure Live Seed ("%PURITY x %GERMINATION / 100 = %PLS" and "lbs/Acre PLS / %PLS x 100 = lbs/Acre Bulk-seed")
• LSU AgCenter — Pure Live Seed Calculation (the same PLS math worked per 1,000 sq ft, plus mixture PLS; turfgrass seeding rates in lb PLS)
• UMass Extension — Understanding a Turfgrass Seed Label (Table 2: seeds per pound, seeding rate, minimum purity and germination, and computed PLS% per species)
• University of Wisconsin-Madison Extension — Pure live seed (plain-language formula and the 85% adjustment threshold; seed coating can cut purity to 66%)
• Purdue Extension AY-25 — Purchasing Quality Grass Seed for Your Lawn (preferred label ranges: purity 90%+, germination 85%+, inert under 8%, tested within 9 months; and how per-component purity reads on a mixture tag)
• Purdue Extension AY-20 — Spring seeding (germination expected once soil temperatures reach 55 F; dormant seeding from Thanksgiving to March)
• Purdue Extension AY-3 — Establishing a lawn (Kentucky bluegrass 1.5-2.0, tall fescue 6.0-9.0 lb/1,000 sq ft; Aug 15-Sep 15 north, Sep 1-30 south)
• NC State Extension — Carolina Lawns (bermudagrass 1-2, zoysiagrass 1-2, centipedegrass 0.25-0.50, bahiagrass 5, tall fescue 6 lb/1,000 sq ft; regional planting dates; coated seed needs a higher rate)
• University of Arkansas FSA-2113 — Seeding rates and dates (bermudagrass 0.5-1.0, centipedegrass 0.25-0.5, zoysiagrass 1.0-2.0, tall fescue 8.0-10.0; "Do not seed bermudagrass after July 1"; bermuda germinates around 63 F)
• UF/IFAS LH013 — Establishing Your Florida Lawn (bahiagrass 5-10, bermudagrass 1-4, centipedegrass 0.25-1 lb/1,000 sq ft)
• Oklahoma State Extension HLA-6419 — Establishing a Lawn in Oklahoma (rates in lb PLS; warm-season seeding at 68-95 F soil, bermuda by July 1; perennial ryegrass 10-12 lb PLS for winter overseeding of bermudagrass)
• Clemson HGIC 1206 — Overseeding with Ryegrass (5 lb per 1,000 sq ft into an established lawn, 10 lb on barren ground)
• Clemson HGIC — Lawn Establishment (seed-quality standard: buy purity 90%+ and germination 85%+; warm-season target date May 1-14, cool-season mid-late September)
• Colorado State University Extension — Buffalograss Lawns (three to five pounds of seed per 1,000 sq ft; will not germinate until soil is above 55 F)
• USDA NRCS Plant Guide — Buffalograss (broadcast seeding rate 3 to 5 pounds per 1,000 sq ft for lawn and residential planting)
• Rutgers NJAES FS584 — Seeding rates and establishment windows (KBG approx 2, tall fescue / fine fescue / perennial ryegrass 4-6 lb/1,000 sq ft; spring seedings need a higher rate than fall)
• NC State Extension Gardener Handbook ch. 9, Lawns (Kentucky bluegrass 1-2 and bermudagrass 1-2 lb/1,000 sq ft, and the coated-seed rule: "If the seed is coated, the seeding rates may need to be doubled")

This calculator is reviewed annually for source currency. About Jake · Last reviewed September 18, 2026.

Embed this tool on your site

Free for lawn-care blogs, garden centres and seed merchants, extension volunteers and master gardener programmes, /r/lawncare and /r/landscaping threads, and personal renovation logs. Required attribution is included in the snippet. No fee, no account, no analytics attached to the embed.

<iframe
  src="https://diyrated.com/grass-seed-calculator/embed/"
  width="100%"
  height="1280"
  loading="lazy"
  style="border:1px solid #e5dcd0; border-radius:16px; max-width:680px;"
  title="Grass Seed Calculator (DIYRated)">
</iframe>
<p style="font-size:12px;color:#666;margin-top:8px">
  Grass seed calculator by
  <a href="https://diyrated.com/grass-seed-calculator/">DIYRated</a>
  &middot; Reviewed by Jake Morrison, Licensed GC
</p>