Grass seed is bought by weight but rated by area: every seeding rate is quoted in pounds per 1,000 square feet, and it changes with the grass type. Divide your lawn area by 1,000, multiply by the rate, and you have the pounds to buy. A 1,000 square foot lawn seeded with tall fescue at 8 pounds per 1,000 needs 8 pounds of seed.
The rate is the whole game, and the two things that move it are the grass species and whether you are starting bare or thickening an existing lawn. Here is how both work.
Seeding rate by grass type
Rates differ this much because seed size differs this much. A pound of Kentucky bluegrass holds around two million seeds; a pound of tall fescue holds roughly a quarter million, so it takes far more weight to cover the same ground:
| Grass type | New lawn | Overseeding |
|---|---|---|
| Kentucky bluegrass | 3 lb / 1,000 sq ft | 1.5 lb |
| Sun and shade mix | 5 lb / 1,000 sq ft | 2.5 lb |
| Tall fescue | 8 lb / 1,000 sq ft | 4 lb |
| Perennial ryegrass | 9 lb / 1,000 sq ft | 4.5 lb |
Always check the bag: blends vary, and the manufacturer's stated rate wins over any general figure. The grass seed calculator applies your chosen rate to your exact lawn size and also tells you how far a 20 pound bag will stretch.
Seed by lawn size
Tall fescue at the 8 pound new-lawn rate, the most common cool-season choice:
| Lawn size | Area | Seed (new lawn) | Seed (overseed) |
|---|---|---|---|
| 20 x 25 ft | 500 sq ft | 4 lb | 2 lb |
| 25 x 40 ft | 1,000 sq ft | 8 lb | 4 lb |
| 50 x 50 ft | 2,500 sq ft | 20 lb | 10 lb |
| 100 x 50 ft | 5,000 sq ft | 40 lb | 20 lb |
Swap in a different species by scaling from the rate table: bluegrass runs a bit over a third of these weights, ryegrass a little more.
More seed is not better
The single most common mistake is overshooting the rate on purpose, on the theory that extra seed means thicker grass. It does the opposite.
Seedlings crowded together compete for the same water, light, and nutrients, and the result is thin, spindly grass that is weak at the root and more prone to damping-off and other fungal disease. You also pay for seed that never becomes healthy turf.
If your number lands between bag sizes, round up modestly and spread the extra over genuinely thin patches rather than lifting the rate everywhere. An even, correct rate beats a heavy one every time.
Rate is only half the job
The pounds get the seed onto the ground; three things decide whether it becomes a lawn:
- Soil contact. Rake seed so it sits within about 1/4 inch of the surface. Seed lying on top or buried too deep will not establish. You should still see roughly half the soil after raking.
- Timing. For the cool-season grasses above (fescue, bluegrass, ryegrass), early fall is best: warm soil, cool air, and a full season before summer stress. Spring is second choice. Warm-season grasses like bermuda are seeded in late spring instead.
- Water. New seed needs the top inch kept consistently moist until germination, which usually means light watering once or twice a day. Letting it dry out once after sprouting is the fastest way to lose a stand.
Prepping the ground first? The topsoil calculator sizes the rooting layer a new lawn needs, and the sod calculator covers the instant-lawn alternative if you would rather skip the germination window.