This lawn seed calculator tells you how much grass seed to buy for a new lawn or an overseeding project — from your area and grass type, at the seeding rates seed companies and extension services actually recommend.
Rate × Area × Job — That’s the Formula
Every grass species has a seeding rate per 1,000 sq ft driven by seed size (bluegrass packs ~1.4 million seeds per pound; tall fescue ~230,000 — hence wildly different poundage for the same coverage). Overseeding runs at half the new-lawn rate because half the “sites” are already occupied. Part of our Ecology Calculators collection.
Worked Example (Verified)
- 5,000 sq ft new tall fescue lawn (defaults): 5 × 8 = 40 lb of seed
- The same lawn overseeded next fall: 20 lb — plus a core aeration first, because seed-to-soil contact is the whole game
- Bluegrass at the same area: only ~15–25 lb (tiny seeds, millions per pound) — buying fescue poundage in bluegrass is a classic expensive mistake that also overcrowds
- Timing note: fall is the premium seeding window for cool-season grasses (warm soil, cool air, fewer weeds); spring seeding works but fights crabgrass season with one hand tied
Germination Reality Checks
- Bag tags list pure seed % and germination % — “PLS” (pure live seed) is their product; bargain bags padded with inert matter and weed seed are no bargain. Serious Bermuda seeding in particular is sold by PLS.
- More seed than rate ≠ thicker lawn: overcrowded seedlings compete, thin out and invite disease. The rate is a ceiling as much as a floor.
- Straw/mulch cover on slopes, pre-germinated seed for impatient ryegrass patches, and irrigation discipline separate the success stories from the reseeds.
- Warm-season grasses (Bermuda, zoysia) often go down as sprigs/plugs or sod instead — sod math is our Turf/Sod-adjacent coverage in the construction collection.
Related Tools
- Fertilizer Calculator — starter fertilizer pairs with new seed
- Garden Soil Calculator — topdressing volumes for leveling
- Ecology Calculators — the full collection
Frequently Asked Questions
How much grass seed do I need for 5,000 square feet?
For a new tall fescue lawn: 40 lb (8 lb per 1,000). Overseeding: 20 lb. Kentucky bluegrass needs far less by weight — roughly 15–25 lb for the same new lawn — because its seeds are far smaller and more numerous per pound. This calculator sets the rate by species and job.
How much seed per 1,000 square feet by grass type?
New-lawn rates: tall fescue 6–8 lb, perennial ryegrass 7–9 lb, Kentucky bluegrass 2–3 lb (pure; blends 3–5), fine fescue 5–6 lb, Bermuda 1–2 lb of pure live seed. Overseeding is half of each. Rates vary a bit by source and blend — the bag’s own label is the final word.
Is it better to overseed in spring or fall?
Fall, decisively, for cool-season lawns: soil is warm for germination, air cools to reduce stress, weed pressure fades, and roots get autumn plus spring to establish before summer. Spring works with earlier timing and a crabgrass plan (pre-emergents block grass seed too — check label compatibility).
Why didn’t my overseeding work?
Usually seed-to-soil contact: seed resting on thatch dries between waterings and never roots. Aerate or dethatch first, mow low, seed, then keep the surface moist for two weeks. The second suspect is rate — a decorative dusting of seed over 5,000 sq ft is bird feed, not a lawn plan.
How long does grass seed take to grow?
Ryegrass 5–10 days, fescue 7–14, bluegrass 14–30 days to germinate under good moisture and soil temperatures above ~50 °F. Full establishment (mowable, rooted turf) takes 6–10 weeks — the patience gap where most lawns get walked on too early.
Is this lawn seed calculator free?
Yes — free, instant, no sign-up.