Formula
Seed needed (lb) = area (sq ft) ÷ 1,000 × seeding rate (lb per 1,000 sq ft). Example: 1,000 sq ft at 5 lb per 1,000 sq ft needs 5 lb of seed.
How to use it, step by step
Measure the lawn area, excluding paths, beds and driveways. Split irregular lawns into rectangles and add them. Find the seeding rate on the seed bag — it differs by grass type and by new lawn vs overseeding. Enter the rate, not a guess: a rate meant for one grass type can be double the rate for another.
Worked example in detail
A 2,500 sq ft lawn at 5 lb per 1,000 sq ft needs 12.5 lb of seed. The same lawn overseeded at 2.5 lb per 1,000 sq ft needs only 6.25 lb. Buying a 25 lb bag for the overseeding job wastes money and tempts you to sow too thickly, which causes weak, disease-prone seedlings competing for light.
What affects real seed needs
Seed quality, soil preparation, watering and birds all affect establishment. Bare soil sown evenly and kept moist germinates far better than seed scattered on dry, compacted ground. Raking seed lightly into the top of the soil and watering daily until germination improves results more than sowing extra seed. In shade, choose a shade-tolerant mix and its own rate, rather than sowing more of a sun mix.
Frequently asked questions
New lawn vs overseeding — why different rates?
A new lawn has no existing grass competing, so it needs a full rate to cover bare soil. Overseeding fills thin patches among existing grass, so a lower rate is enough and avoids overcrowding.
Should I add extra seed as insurance?
A small buffer, about 10%, is sensible for edges and patchy areas. Doubling the rate is not insurance — it is overcrowding.
When should I sow?
Cool-season grasses establish best in early autumn or spring, warm-season grasses in late spring to early summer, when soil is warm. Follow local extension guidance for your grass type and region.