How much grass seed do I need?
Seed is sold by the pound and recommended by the pound per 1,000 square feet, so the math is the same as fertilizer: rate × (area ÷ 1,000). The rate depends on two things — the species (bluegrass seed is tiny, fescue seed is big, so the pounds differ four-fold for the same number of plants) and whether you're starting from bare soil or thickening an existing lawn.
Overseeding 5,000 sq ft of tall fescue at 3.5 lb per 1,000 = 17.5 lb. A new tall fescue lawn on the same area, at 7 lb per 1,000, needs 35 lb. Bluegrass on that new lawn: 12.5 lb — a quarter of the weight for the same job.
Seeding rates by grass type
| Grass | Season | New lawn lb / 1,000 sq ft | Overseed lb / 1,000 sq ft | New lawn, 5,000 sq ft | Overseed, 5,000 sq ft |
|---|---|---|---|---|---|
| Kentucky bluegrass | Cool | 2.5 | 1.25 | 12.5 lb | 6.3 lb |
| Tall fescue | Cool | 7 | 3.5 | 35.0 lb | 17.5 lb |
| Fine fescue | Cool | 4.5 | 2.5 | 22.5 lb | 12.5 lb |
| Perennial ryegrass | Cool | 7 | 3.5 | 35.0 lb | 17.5 lb |
| Cool-season mix / sun & shade blend | Cool | 5 | 2.5 | 25.0 lb | 12.5 lb |
| Bermudagrass | Warm | 1.5 | 0.75 | 7.5 lb | 3.8 lb |
| Zoysiagrass | Warm | 1.5 | 0.75 | 7.5 lb | 3.8 lb |
| St. Augustine | Warm | — | — | sod / plugs | sod / plugs |
| Centipedegrass | Warm | 0.4 | 0.25 | 2.0 lb | 1.3 lb |
| Bahiagrass | Warm | 7.5 | 4 | 37.5 lb | 20.0 lb |
Midpoints of the ranges in university extension establishment guides (Penn State, UGA, Clemson HGIC). Published ranges run about ±30% around these; a seed blend's tag may state its own rate — use it if it does.
New lawn vs overseeding: why half
On bare soil every plant has to come from seed, so the rate is set to give full cover fast enough to beat weeds. When you overseed, the existing turf is already doing most of that, and seed dropped into it competes for light; half the new-lawn rate gives the seedlings room without wasting the other half under a canopy where it can't establish. A thin lawn being renovated — more dirt than grass — is a new lawn for rate purposes. If you're honestly not sure, rate by the worst third of the lawn, not the best.
Read the tag: pure live seed
Every bag sold in the US carries a tag listing each variety's purity (% of the weight that's that seed) and germination (% of those seeds that sprouted in a lab test), plus other crop, weed seed and inert matter. Multiply germination by purity and you have pure live seed — the fraction of each pound that can actually become grass. Published seeding rates assume good seed, roughly 80% PLS; a bag that's worse needs proportionally more pounds, and the calculator adjusts for it if you enter the tag numbers.
A typical tag (85% germination, 95% purity) is 81% PLS and the overseed comes to 17.3 lb. A bargain bag at 70/90 is 63% PLS and needs 22.2 lb for the same result. A coated bag with 50% coating needs 35.0 lb of product — twice the weight — because half of every scoop is clay.
Coated seed: you're buying half coating
Coated seed — the blue or green pellets in the "water-smart", "with mulch" bags — wraps each seed in a clay or polymer layer that holds moisture and makes it easier to see where you've spread. Those are real benefits for a hand-seeded patch. But the coating is typically 40–50% of the bag by weight, the tag will say so under "inert matter" or "coating material", and the coverage printed on the front already assumes you're spreading the heavier pellet. Enter the coating % and the calculator shows the pounds of product you actually have to buy; the cost table below shows what that does to the price per pound of live seed.
Bags and the honest cost per pound
| Bag (example price) | $ per lb of bag | Tag | $ per lb of live seed |
|---|---|---|---|
| Premium tall fescue blend, 20 lb — $90 | $4.50 | 90/98 | $5.10 |
| Big-box "sun & shade" mix, 7 lb — $25 | $3.57 | 85/95 | $4.42 |
| Coated "water-smart" fescue, 7 lb — $28 | $4.00 | 85/95, 50% coated | $9.91 |
| Bargain contractor mix, 25 lb — $45 | $1.80 | 75/90 | $2.67 |
Illustrative prices; the live-seed column divides price by (bag weight × (1 − coating) × germination × purity). Enter your own bag above.
The pattern holds at most stores: the premium bag that looks expensive per pound is usually the cheapest per pound of seed that will grow, and the small coated bag that looks convenient is the dearest. Buy by the tag, not the front of the bag.
When to seed
Cool-season grasses (bluegrass, fescue, rye) establish best in late summer and early fall — warm soil, cooling air, and two growing seasons before the seedlings meet their first July. Spring seeding works but fights crabgrass pre-emergent and summer heat. Warm-season grasses seed in late spring once soil passes about 65 °F. The Lawn Care Planner dates the window for your zone; for a cool-season lawn the overseeding window it produces is:
| Zone | Aerate & overseed window |
|---|---|
| 4 | Aug 7 – Sep 5 |
| 5 | Aug 25 – Sep 23 |
| 6 | Sep 1–30 |
| 7 | Sep 14 – Oct 13 |
| 8 | Sep 27 – Oct 26 |
Planner output for a tall fescue lawn at each zone's typical first-frost date; your own frost date refines it.
After it's down
Seed-to-soil contact and moisture decide whether the pounds you bought become grass. Rake or core-aerate first, spread half the seed one way and half crosswise, rake lightly again, and keep the top half inch damp — light watering once or twice a day until germination (a week for rye, two for fescue, three or more for bluegrass), then taper to deeper, less frequent watering. A starter fertilizer with phosphorus is one of the few times P is justified on turf; the button above carries your area to the fertilizer calculator.
Sources: Penn State Extension, Lawn Establishment; UGA Extension, Lawns in Georgia: Selection and Establishment; Clemson HGIC, Selecting a Lawn Grass and Overseeding; AOSA / Federal Seed Act labeling requirements for purity and germination.