Area 1
Seed quality and cost
On the seed tag. Premium 95–99%.
On the seed tag. Premium 85–95%.
Edges, overlap, reseeding misses.
0 to use the species default.
Our grass seed calculator works out exactly how much grass seed you need. Enter your lawn size, choose your grass type, and it gives you the pounds and the number of bags — for a new lawn, for overseeding, or for filling bare patches.
The short answer
Grass seed is measured in pounds per 1,000 square feet, and the rate depends on the grass. Tall fescue needs 6–8 lb, Kentucky bluegrass only 2–3, and Bermuda just 1–2.
The formula is lawn area ÷ 1,000 × seeding rate. A 5,000 ft² new lawn in tall fescue needs about 35 lb. Overseeding the same lawn needs about half that.
On this page
How to use this grass seed calculator
Measure your lawn and enter it. You can add several areas and use rectangles, circles, triangles, or a square footage you already know — useful for lawns that aren’t a simple shape.
Then set three things:
- What you’re doing — new lawn, overseeding, or bare patches. This halves or doubles the rate
- Grass type — rates vary by more than 10× between species
- Ground conditions — slopes and shade both need extra seed
Under Seed quality and cost you can enter the purity and germination figures from the seed tag, which is how you find out what a bag is really worth.
The formula
Pounds of seed = Lawn area ÷ 1,000 × Seeding rate
Rate in lb per 1,000 ft² · halve it for overseeding
Worked example — 80 × 60 ft lawn, new, tall fescue
Seeding rates by grass type
| Grass type | New lawn | Overseeding | Seeds per lb | Season |
|---|---|---|---|---|
| Kentucky bluegrass | 2–3 lb | 1.25 lb | 2,200,000 | Cool |
| Fine fescue | 4–5 lb | 2.25 lb | 450,000 | Cool, shade |
| Tall fescue | 6–8 lb | 3.5 lb | 230,000 | Cool |
| Perennial ryegrass | 6–9 lb | 3.75 lb | 250,000 | Cool |
| Annual ryegrass | 7–8 lb | 3.75 lb | 215,000 | Temporary |
| Bermuda, hulled | 1–2 lb | 0.75 lb | 1,500,000 | Warm |
| Zoysia | 1–2 lb | 0.75 lb | 1,300,000 | Warm |
| Centipede | 0.25–0.5 lb | 0.2 lb | 400,000 | Warm |
| Bahia | 5–10 lb | 3.75 lb | 170,000 | Warm |
All rates in pounds per 1,000 square feet.
The range between centipede at a quarter pound and bahia at ten pounds is 40 times. Using a single generic rate for “grass” is the biggest source of error there is.
New lawn vs overseeding
New lawn
Full rate
Bare soil, nothing to compete with. Every plant in the finished lawn comes from what you sow.
Overseeding
Half rate
You’re filling gaps in existing turf. The established grass outcompetes most of what you sow, so a full rate is wasted.
Bare patches
Full rate
Even within an existing lawn, genuinely bare spots are new lawns in miniature. Half rate leaves them thin.
The half-rate rule for overseeding is consistent across every source and extension service. It exists because seed landing in established turf mostly doesn’t reach soil, and what does reach soil competes with mature grass that has a full root system already.
Scratch the surface first. Seed broadcast onto compacted bare soil largely feeds birds — it needs contact with soil to root. Rake, scarify or core-aerate before you spread.
The bag label trap
This catches people constantly. You buy to the coverage figure on the bag, spread it over bare soil, and end up with a thin patchy lawn — because that figure assumed you were overseeding.
On a 5,000 ft² new lawn in tall fescue, the correct quantity is 35 lb. The label rate gives 18 lb — you’re half short.
Before you buy, check whether the bag’s coverage figure says “new lawn” or “overseeding”. If it doesn’t say, assume overseeding and double it.
Pure live seed — what’s really in the bag
Every bag of grass seed carries a tag with two percentages, and together they tell you how much of that bag will actually become grass.
PLS = Purity % × Germination %
Everything else is inert matter, other seed, or seed that will never come up
| Seed tag | Pure live seed | Extra seed needed | Quality |
|---|---|---|---|
| 98% purity × 90% germination | 88.2% | ×1.13 | Premium |
| 95% × 85% | 80.8% | ×1.24 | Good |
| 90% × 85% | 76.5% | ×1.31 | Average |
| 85% × 80% | 68.0% | ×1.47 | Budget |
A budget bag at 85/80 needs 30% more seed than a premium bag at 98/90 to put the same amount of live seed on the ground. So a bag that’s 20% cheaper per pound isn’t cheaper at all.
Compare bags on cost per pound of live seed, not cost per pound. Enter the tag figures in the calculator and it does the adjustment for you. Cheap seed also tends to carry more weed seed and more “other crop” — which is how you end up weeding a brand new lawn.
Why rates differ so much
Two things drive it, and most explanations only mention the first.
Seed size. Kentucky bluegrass has around 2.2 million seeds per pound; tall fescue has 230,000. A pound of bluegrass contains nearly ten times as many seeds.
Growth habit — and this matters more than people realise:
| Habit | Grasses | What it means |
|---|---|---|
| Spreading | Kentucky bluegrass, Bermuda, zoysia | Sends out runners and fills gaps itself |
| Bunch | Tall fescue, ryegrass | Grows in clumps. Does not spread at all |
A bunch grass has no mechanism to fill a gap. Every plant in the finished lawn has to come from a seed you sowed, which is why tall fescue needs 7 lb per 1,000 ft² against bluegrass at 2.5.
Spreading grasses knit over small gaps on their own within a season. Fescue and ryegrass never will — so sow evenly, and don’t skimp on coverage in the hope it fills in.
Bag coverage
| Bag | Bluegrass at 2.5 lb | Tall fescue at 7 lb | Bermuda at 1.5 lb |
|---|---|---|---|
| 25 lb | 10,000 ft² | 3,571 ft² | 16,667 ft² |
| 50 lb | 20,000 ft² | 7,143 ft² | 33,333 ft² |
The same 50 lb bag covers 7,143 ft² of tall fescue or 33,333 ft² of Bermuda. This is why “how many bags do I need” has no answer without knowing the grass.
Seed keeps for two to three years in a cool dry place, so a little over is not wasted — and you’ll want some for reseeding spots that don’t take.
When to sow
| Grass | Best window | Germination |
|---|---|---|
| Cool-season — fescue, bluegrass, rye | Early autumn, then spring | 5–30 days |
| Warm-season — Bermuda, zoysia | Late spring to early summer | 10–30 days |
Early autumn is the strongest window for cool-season grass: soil is still warm, air is cooling, and weed competition has dropped. It also gives the new grass two cool seasons to establish before summer stress.
Germination speed varies a lot: perennial ryegrass in 5–10 days, tall fescue 7–14, fine fescue 10–14, Kentucky bluegrass 14–30. Bluegrass being slowest is why it’s often blended with ryegrass — the rye covers the ground while the bluegrass establishes.
Whatever you sow, keep the top inch consistently moist until germination — usually light watering twice a day. Letting seed dry out once after it has swollen kills it, and that’s the most common reason a correctly-calculated sowing fails.
Grass seed mistakes to avoid
- Using one generic rate. Species rates differ by up to 40 times.
- Buying to the bag’s coverage figure for a new lawn. It’s usually the overseeding rate.
- Ignoring purity and germination. Budget seed needs 30% more.
- Overseeding at the full rate. Established grass outcompetes it; it’s wasted.
- Half rate on genuinely bare patches. Those need the full new-lawn rate.
- Sowing onto compacted soil. Scratch the surface first.
- Sowing more than the rate “to be safe”. Crowded seedlings compete and thin out.
- Letting seed dry out once. After it swells, drying kills it.
- Expecting fescue to fill gaps. Bunch grasses never spread.
Frequently asked questions
How much grass seed do I need?
Lawn area ÷ 1,000 × the seeding rate for your grass. Tall fescue needs 6–8 lb per 1,000 ft², Kentucky bluegrass 2–3, Bermuda 1–2. A 5,000 ft² new lawn in tall fescue needs about 35 lb. Overseeding the same lawn takes about half.
How much grass seed per 1,000 square feet?
It depends entirely on the grass. Kentucky bluegrass 2–3 lb, fine fescue 4–5, tall fescue 6–8, perennial ryegrass 6–9, hulled Bermuda 1–2, centipede just 0.25–0.5. Halve all of these for overseeding.
How much seed do I need for overseeding?
About half the new-lawn rate — so 3.5 lb per 1,000 ft² for tall fescue rather than 7. You’re filling gaps in existing turf, and established grass outcompetes most of what you sow, so a full rate is largely wasted. Genuinely bare patches still need the full rate.
How many square feet does a 50 lb bag of grass seed cover?
Depends on the grass. At tall fescue’s 7 lb per 1,000 ft² a 50 lb bag covers 7,143 ft². At Kentucky bluegrass rates it covers 20,000 ft², and at Bermuda rates 33,333. The bag’s own coverage figure usually assumes overseeding.
What is pure live seed?
Purity multiplied by germination — the share of a bag that will actually become grass. A premium bag at 98% purity and 90% germination is 88% PLS. A budget bag at 85/80 is only 68%, so it needs 30% more seed for the same result. Compare bags on cost per pound of live seed.
Why does the bag say a different amount than this calculator?
Most bags print the overseeding rate rather than the new-lawn rate, so for bare soil the label figure is roughly half what you need. Bag rates also assume ideal purity and germination. Check whether the label says “new lawn” or “overseeding” — if it doesn’t say, assume overseeding.
Why do different grasses need such different amounts?
Seed size and growth habit. Kentucky bluegrass has 2.2 million seeds per pound against tall fescue’s 230,000. Bluegrass also spreads by runners and fills gaps itself, while tall fescue is a bunch grass that never spreads — so every plant must come from a seed you sowed.
Can I use too much grass seed?
Yes. Overcrowded seedlings compete for water, light and nutrients, producing weak thin turf that’s prone to disease and often dies back within weeks. More seed does not mean a thicker lawn — the correct rate is the one that gives each seedling room.
When is the best time to plant grass seed?
Early autumn for cool-season grasses like fescue, bluegrass and ryegrass — warm soil, cooling air, less weed competition, and two cool seasons to establish before summer. Warm-season grasses like Bermuda and zoysia go in late spring to early summer.
How long does grass seed take to germinate?
Perennial ryegrass is fastest at 5–10 days, tall fescue 7–14, fine fescue 10–14, and Kentucky bluegrass slowest at 14–30. Keep the top inch consistently moist throughout — letting seed dry out once after it swells kills it.
Do I need more seed on a slope?
Yes, roughly 15–20% more, because seed washes downhill before it roots. Shaded areas also need about 20% extra. The calculator adjusts for both. On steep slopes consider an erosion blanket or hydroseeding rather than simply adding seed.
Can I use this grass seed calculator in metric?
Areas are entered in feet and rates given in pounds per 1,000 square feet. To convert, multiply square metres by 10.76 for square feet, and pounds by 0.4536 for kilograms. As a guide, 1 lb per 1,000 ft² is about 4.9 grams per square metre.
Sources and method
- Seeding rates compiled from turfgrass extension guidance and commercial seed supplier rate charts, using the midpoint of the published range for each species
- The half-rate rule for overseeding is consistent across extension services and seed suppliers
- Seed counts per pound are typical values and vary by cultivar — Kentucky bluegrass in particular ranges from about 900,000 to 2.2 million
- Pure live seed is purity × germination, the standard agronomic adjustment; both figures appear on the seed tag by law in the US
- Slope and shade allowances are practical field adjustments rather than published standards
- Local extension services give the best regional advice on species selection and timing — conditions vary far more than rates do
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How this grass seed calculator works out its numbers
The base rate is the midpoint of the published range for your species. Overseeding halves it; bare patches use the full new-lawn rate, since those spots are new lawns in miniature regardless of what surrounds them.
Ground conditions apply next — 17.5% extra on slopes where seed washes, 20% in shade, and 35% where both apply. The pure live seed adjustment then divides by purity × germination, because a bag that’s 68% live seed has to be spread more heavily to put the same live seed on the ground. The spreading allowance is applied last, covering edges, overlap and the spots that don’t take.
Seed counts per square foot are shown as a sanity check. If that number looks wildly different from what you’d expect, it usually means the wrong species is selected.
Rates are agronomic guidance, not a guarantee. Cultivars vary, seed counts per pound differ within a species, and local conditions matter more than any table. Your regional extension service will give better advice on species selection and timing than a general calculator can. Sowing at the right rate is only part of it — soil contact, consistent moisture through germination, and the right season do more for the result than the last pound of seed.