Lawn Seed Calculator
How much grass seed a new lawn or an overseeding job needs — pounds by grass type at the published seeding rates, and the bags to buy.
Seeding rates are the whole calculation
Grass seed is not sold by the lawn — it is applied by the pound, at a rate set by the grass type. Small-seeded grasses like Kentucky bluegrass pack hundreds of thousands of seeds into a pound and go down light; big-seeded fescue needs pounds where bluegrass needs ounces of seed count. The calculator uses the published seeding rates turf programs and extension services print for each grass, full rate for a new lawn and half rate for overseeding into an existing one.
Pounds = (area ÷ 1,000) × rate for the grass · Overseeding = half the new-lawn rate
Example: a 100 × 50 ft lawn is 5,000 sq ft. Tall fescue at 8 lb per 1,000 sq ft needs 40 lb of seed — 44 lb with the 10% allowance, so one 50 lb bag covers it with seed left for the thin spots.
| Grass | New lawn (lb / 1,000 sq ft) | Overseeding (lb / 1,000 sq ft) |
|---|
| Tall fescue | 8 | 4 |
| Kentucky bluegrass | 3 | 1.5 |
| Perennial ryegrass | 8 | 4 |
| Bermudagrass | 2 | 1 |
Two field notes. First, seed-to-soil contact decides germination more than the exact poundage — rake or slit-seed overseeding in rather than broadcasting onto thatch. Second, blends change the maths: a bag that is 50% bluegrass by weight carries its rate with it, so when a blend's label prints its own seeding rate, the label wins over this table.
Frequently asked questions
When is the best time to seed a lawn?
For cool-season grasses (fescue, bluegrass, ryegrass), early fall is the strongest window — warm soil, cool air, fewer weeds — with early spring second. Bermudagrass and other warm-season grasses go down in late spring into early summer, once soil is properly warm.
Can I just throw extra seed down to be safe?
Up to a point. Seed much beyond the printed rate germinates into a crowd of weak seedlings competing for the same water and light, and the stand thins itself out diseased. The published rate plus a modest allowance is the sweet spot — which is why the calculator adds 10%, not 50%.
How long does grass seed take to germinate?
Ryegrass is fastest at 5–10 days, tall fescue 7–14, bermudagrass 10–30, and Kentucky bluegrass the slowest at 14–30 days. Keep the seedbed evenly moist the whole time — one dry afternoon can end the slow seeds.
Does overseeding really use half the seed?
Yes — an overseeding pass is filling gaps in an existing stand, not building one, so half the new-lawn rate is the standard recommendation. Dethatching or aerating first so the seed reaches soil matters more than adding extra pounds.
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