Grass Seed Calculator
Pounds of seed by lawn size, grass type, and seeding rate.
You need
8.0 lb
Rates vary by blend; check the bag and use its number if it differs.
- Lawn area
- 1,000 sq ft
- A 20 lb bag covers
- 2,500 sq ft
Estimates only. Verify quantities before ordering.
How this is calculated
Seed = lawn area / 1,000 x rate for the selected grass and job. Rates: tall fescue 8 lb new or 4 lb overseed, Kentucky bluegrass 3 lb new, perennial ryegrass 9 lb new, sun and shade mix 5 lb new, per 1,000 sq ft.
Enter the lawn dimensions and pick the grass type and job, and this calculator converts the standard seeding rate (pounds per 1,000 square feet) into the total seed to buy. New lawns use roughly double the overseeding rate because bare soil needs full coverage, while overseeding just thickens what is already growing.
More seed is not better. Seeding far above the recommended rate crowds seedlings into weak, spindly grass that is more prone to disease, and it wastes money. If your number lands between bag sizes, round up modestly and spread the extra over thin areas rather than doubling the rate everywhere.
Seed for common lawn sizes
Rows show tall fescue at the new-lawn rate of 8 lb per 1,000 sq ft; overseeding uses about half.
| Lawn size | Seed | Area |
|---|---|---|
| 20 x 25 ft (500 sq ft) | 4.0 lb | 500 sq ft |
| 25 x 40 ft (1,000 sq ft) | 8.0 lb | 1,000 sq ft |
| 50 x 50 ft (2,500 sq ft) | 20.0 lb | 2,500 sq ft |
| 50 x 100 ft (5,000 sq ft) | 40.0 lb | 5,000 sq ft |
| 100 x 100 ft (10,000 sq ft) | 80.0 lb | 10,000 sq ft |
Seeding rates: new lawn versus overseeding
New lawns take roughly twice the seed of an overseed, because there is no existing turf sharing the space. Typical figures for a new lawn run about 6 to 8 pounds per thousand square feet for tall fescue, 2 to 3 for Kentucky bluegrass, and 5 to 7 for perennial ryegrass. Overseeding an established lawn uses about half those rates. Bluegrass looks low against the others only because its seed is far smaller, so a pound contains many more seeds.
More seed is not better. Sowing heavily produces dense seedlings that compete with each other for water and light, and the resulting stand is weak and prone to disease rather than lush. The rate on the bag is the result of testing, and doubling it wastes money and produces a worse lawn. Spread half the seed walking in one direction and the other half walking across it to get even coverage without overlap stripes.
Seed mixes, blends, and what the label tells you
A blend is several varieties of the same species; a mixture combines different species. Both exist for a reason: monocultures are vulnerable, and a mixture that includes a fast-germinating ryegrass alongside a slower bluegrass gives quick cover while the slower grass establishes underneath. For a mixed sun and shade yard, a mixture is usually more forgiving than a single species chosen for the average condition.
The seed label is the most useful and least read part of the bag. It states the percentage of each variety, the germination rate, and crucially the percentages of inert matter, other crop seed, and weed seed. Cheap seed is cheap because it carries more filler and a lower germination rate, so a bag covering half the area at twice the quality is often the better buy. Check the test date too, since germination falls off as seed ages.
Timing beats everything else
For cool-season grasses, late summer into early fall is by a wide margin the best window. The soil is still warm enough for fast germination, nights are cooling, rainfall is more reliable, and annual weeds are finishing rather than starting. Spring seeding works but puts young grass into summer heat with a shallow root system, competing against crabgrass at its most aggressive. Warm-season grasses invert this: seed them in late spring or early summer once soil temperatures are consistently warm.
Seed needs contact with soil, not a layer of thatch or leaves, and it needs to stay damp until it germinates. That means light watering once or twice a day for the first couple of weeks rather than deep soaking, then tapering as the seedlings root. One dry afternoon at the wrong moment kills germinating seed outright, which is why a fall seeding in a rainy stretch outperforms a technically perfect spring one.
Common questions
How much grass seed per square foot?
Rates are quoted per 1,000 square feet and differ by species because seed sizes differ enormously. Tall fescue runs about 8 lb per 1,000 for a new lawn, perennial ryegrass 8 to 10, but Kentucky bluegrass only 2 to 3 because its seed is tiny. Overseeding uses about half the new-lawn rate.
When is the best time to plant grass seed?
For the cool-season grasses this calculator covers (fescue, bluegrass, ryegrass), early fall is best: warm soil, cooler air, and a full season before summer stress. Spring is second best. Warm-season grasses like bermuda are seeded in late spring instead.
Why is bluegrass seeded so much lighter than fescue?
Kentucky bluegrass seed is far smaller, so a pound contains around two million seeds versus roughly a quarter million for tall fescue. Bluegrass also spreads by rhizomes and fills in on its own, while fescue is a bunch grass that only thickens where seed actually lands.
Should I put topsoil or straw over new seed?
Seed wants firm contact with soil, not burial: rake it lightly so it sits within about 1/4 inch of the surface. A thin scattering of clean straw or a seeding mulch helps hold moisture on slopes and hot sites, but you should still see about half the soil through it.