Grass Seed Calculator
Work out how much grass seed a new lawn or an overseeding job needs, by grass type.
Grass seed is sold by the bag and sown by the pound per thousand square feet, and the right rate changes fivefold between grass types: bluegrass seed is dust, ryegrass is coarse. Too little seed leaves a thin lawn that weeds move into; too much wastes money and crowds seedlings into disease. This calculator matches the rate to the grass and the job.
Measure the lawn area honestly, excluding beds, paths and the house footprint. If the patch is really a bed in disguise, the Topsoil Calculator is the better tool for what goes there instead.
How this is worked out
Pounds of seed = area / 1,000 x rate for the grass. Rates are seeds-per-pound in disguise: Kentucky bluegrass carries around a million seeds per pound, so 2.5 to 4 lb covers the ground; perennial ryegrass has about a fifth as many seeds per pound and needs 7 to 9 lb for the same coverage. Overseeding halves the rate because half the ground is already grass.
Assumptions:
- Rates assume good seed-to-soil contact on prepared ground. Seed broadcast on thatch or hardpan needs the top of the range, and a slit seeder beats a spreader.
- Blends follow the rate of their main component by weight, which the bag tag lists. A bluegrass and ryegrass blend usually sows at 4 to 5 lb per 1,000 sq ft.
- Bag coverage claims on packaging assume ideal spreading; buying for the top of the range covers real-world loss.
Worked examples
1. A 5,000 sq ft new tall fescue lawn. At 7 to 9 lb per 1,000 sq ft: 35 to 45 lb of seed, so three 20 lb bags, with the third opened partway.
2. Overseeding 3,000 sq ft of bluegrass. Full rate 2.5 to 4, halved: 3.75 to 6 lb. One 5 lb bag is close; a 10 lb bag leaves next year’s patch seed.
3. A 1,000 sq ft ryegrass winter overseed in the South. 7 to 9 lb for the patch. Ryegrass is the overseeding standard because it germinates in a week and dies out on schedule in summer heat.
Seeding rates at a glance
| Grass | New lawn, lb per 1,000 sq ft | Germination |
|---|---|---|
| Kentucky bluegrass | 2.5 to 4.0 | 14 to 30 days |
| Perennial ryegrass | 7.0 to 9.0 | 5 to 10 days |
| Tall fescue | 7.0 to 9.0 | 7 to 21 days |
| Fine fescue | 4.0 to 5.0 | 14 to 21 days |
| Bermudagrass (hulled) | 1.5 to 2.0 | 7 to 14 days |
| Zoysiagrass | 2.0 to 3.0 | 14 to 28 days |
| Buffalograss | 3.0 to 4.0 | 14 to 30 days |
| Centipedegrass | 0.5 to 1.0 | 14 to 21 days |
Germination speed matters for overseeding: fast ryegrass beats the weeds to the light, while slow bluegrass needs the existing lawn scalped and the seed kept moist for nearly a month.
Common mistakes
- Sowing by the bag’s coverage claim. Bag claims use the bottom of the rate range on perfect ground. Work from pounds per 1,000 sq ft instead.
- All the seed in one direction. Spreader patterns stripe. Half rate in each of two crossing passes is the classic fix.
- Seed on thatch. Seed that never touches soil never germinates. Dethatch or slit-seed first, then roll or tread the seed in.
- Letting it dry once. Germinating seed that dries out dies, unlike established grass. Keep the top half inch moist until seedlings are up, even if that means light watering twice a day.
Putting the result to work
Sow when soil is warm and rain is plausible: early fall is the prime window for cool-season grasses, late spring for warm-season types. Cover with a whisper of straw or compost on slopes, water lightly and often until germination, then stretch the intervals. The first mow waits until seedlings reach 3 to 4 in, and takes off no more than a third. For the watering schedule in gallons, the Garden Watering Calculator converts the area into weekly water.
How much grass seed do I need?
- Measure the lawn area in square feet, excluding beds, paths and buildings.
- Pick the grass type; its seeding rate in pounds per 1,000 sq ft does most of the work.
- Choose new lawn for the full rate, or overseeding for half rate.
- Buy for the top of the range; leftover seed keeps a year in a cool dry place for patching.
- Sow in two crossing passes, keep the seedbed moist until germination, and mow first at 3 to 4 inches.
How much grass seed do I need per 1,000 square feet?
It depends on the grass: 2.5 to 4 lb for Kentucky bluegrass, 7 to 9 lb for perennial ryegrass or tall fescue, 4 to 5 lb for fine fescue, and 1.5 to 2 lb for bermudagrass. The difference is seed size: small-seeded grasses carry far more seeds per pound, so fewer pounds cover the same ground.
How much seed for overseeding versus a new lawn?
About half the new lawn rate. The existing grass already covers half the ground and shelters the new seed, so 3.5 to 4.5 lb per 1,000 sq ft of tall fescue, or 1.25 to 2 lb of bluegrass, is the usual overseeding range.
Can I put down too much grass seed?
Yes. Seedlings sown far past the top of the range compete for light and water, stay spindly, and invite damping-off disease. More seed than the range is worse than the middle of it, not better.
How long does grass seed keep?
About two to three years in a cool, dry place, losing roughly 10 percent germination per year. Old seed can still be used: sow it at the top of the range, or a little above, to make up the loss. A damp rag test of 100 seeds tells you the real rate.
When is the best time to sow grass seed?
Early fall for cool-season grasses (bluegrass, fescue, ryegrass): warm soil, cool air, fewer weeds, and rain that helps instead of bakes. Late spring is second best. Warm-season grasses (bermuda, zoysia, centipede) go the other way: late spring into early summer, once soil passes about 65 F.
Seeding rates follow common US extension turf guidance per grass species. Rates are pounds of pure live seed per 1,000 sq ft for a new lawn; overseeding at half rate is the standard planning figure.
