Grass Seed Calculator
Last updated August 21, 2026 · checked against our testing process
Your lawn
Seed needed
How to use the grass seed calculator
- Measure the area — lawn square footage, minus beds and hardscape.
- Pick your grass type — seeding rates differ 5× between species; Bermuda needs a fraction of what fescue does.
- New lawn or overseed — overseeding uses half the new-lawn rate.
- Spread in two passes — half the seed each direction, perpendicular, for even germination.
How much grass seed per square foot?
Rates are quoted per 1,000 sq ft and vary hugely by species: tall fescue wants 8 lb/1,000 for a new lawn while Bermuda needs 1.5 - a 4,000 sq ft yard needs anywhere from 6 to 32 lb depending on what you plant. Overseeding halves every rate. This calculator applies the right rate for five common types so you buy one correct bag instead of two wrong ones.
The over-seeding trap (the other kind)
Doubling the rate produces a worse lawn: seedlings compete for light and water, grow spindly, and thin dramatically by month three. Hit the rate, prep the soil (¼" of loosened surface or a topdress - see the topsoil calculator), keep it damp for 2–3 weeks, and density comes from tillering, not seed volume.
Timing beats everything
Cool-season grasses (bluegrass, fescue, rye): late summer to early fall, soil 50–65°F - spring is second-best. Warm-season (Bermuda): late spring, soil 65°F+. Seeding against the calendar wastes most of the bag regardless of rate.
Reading the label: PLS vs. bulk weight
Every lb/1,000 rate above assumes 100% pure live seed (PLS), but no bag hits that. Check the tag for purity% and germination%, then multiply them: 85% purity × 90% germination = 76.5% PLS. A species that needs 8 lb/1,000 sq ft in true PLS terms actually requires 8 ÷ 0.765 ≈ 10.5 lb of that specific bag to hit the real rate. Cheap bulk-blend bags often run well below that figure, widening the gap further - buying by bag weight alone, without doing this division, can leave a lawn noticeably underseeded even when the label number matches the calculator.
Shade, slope, and disturbed soil all push the rate up
The base rates assume full sun and level, freshly prepped soil. Shade under a tree canopy (under roughly 4 hours of direct sun) calls for extra seed - even a shade-tolerant fine fescue mix germinates at a lower percentage than it would in full sun. Slopes steeper than about 3:1 lose a meaningful share of broadcast seed to runoff and bird predation before it roots - add the same kind of margin, or switch to a hydroseed slurry, which locks seed against the soil and needs less overage than dry broadcast. Bare, compacted, or eroded patches inside an otherwise established lawn should be seeded at the new-lawn rate, not the overseed rate, regardless of what the surrounding turf looks like.
The two inputs the seed rate alone doesn't cover
Straw cover: one standard straw bale covers about 1,000 sq ft at a light rate - soil should still show through the mulch, not be fully hidden - piling it thicker smothers seedlings instead of protecting them, and a tackifier spray is the usual substitute on slopes where straw slides. Starter fertilizer: apply a phosphorus-heavy starter (a ratio like 10-20-10) at roughly 1 lb of actual phosphorus, not product weight, per 1,000 sq ft at seeding time, then hold off on high-nitrogen feeding until after the third mow so roots establish before top growth does. Skipping either of these is a common reason a correctly-rated seed job still comes in patchy.
Related tools
Instant option: the sod calculator for the same area. Prep layer: topsoil. Beds and edges: mulch calculator.
Standards and references
Seeding rates in this calculator come from the NTEP (National Turfgrass Evaluation Program) variety-specific establishment tables and are echoed in state cooperative-extension bulletins. Kentucky bluegrass: 2-3 lb per 1,000 sq ft. Tall fescue: 6-8 lb. Perennial ryegrass: 6-9 lb. Bermudagrass: 1-1.5 lb.
Frequently Asked Questions
How much grass seed for 1,000 sq ft?
New lawn: 3 lb bluegrass, 8 lb tall fescue, 5 lb ryegrass, 1.5 lb Bermuda. Overseeding: half those rates.
Can I use too much grass seed?
Yes — overcrowded seedlings compete and thin out badly. Stick to the rate; density comes from healthy plants spreading.
When should I plant grass seed?
Cool-season: late Aug–Sep (best) or spring. Warm-season: late spring once soil passes 65°F.
How long until grass seed grows?
Ryegrass 5–7 days, fescue 7–14, bluegrass 14–28. Full mowable lawn in 6–10 weeks with steady moisture.