Grass Seed Calculator
How many pounds of seed your lawn needs, by species, for either a new seeding or an overseed. The rates differ by a factor of sixteen between species, so the choice matters.
How much grass seed do I need?
Seeding rates are quoted in pounds per 1,000 square feet, and they vary wildly by species because seed size varies wildly. Kentucky bluegrass seed is tiny, so 2 pounds covers 1,000 square feet. Tall fescue seed is four times the size, so the same coverage takes 8 pounds. Centipede is finer still at half a pound.
That is a sixteenfold spread between the lightest and heaviest rates on this page. Using a generic number is how people end up either wasting several hundred dollars of seed or wondering why their lawn came in patchy.
| Species | New lawn, lb per 1,000 sq ft | Overseed, lb per 1,000 sq ft | Season |
|---|---|---|---|
| Kentucky bluegrass | 2 | 1.5 | Cool |
| Tall fescue | 8 | 4 | Cool |
| Perennial ryegrass | 8 | 5 | Cool |
| Fine fescue | 5 | 3 | Cool |
| Bermuda (hulled) | 2 | 1 | Warm |
| Zoysia | 2 | 1 | Warm |
| Centipede | 0.5 | 0.25 | Warm |
| Bahia | 8 | 5 | Warm |
More seed does not make a thicker lawn
This is the most common and most expensive mistake in lawn seeding. It feels intuitive that doubling the seed doubles the density. It does the opposite.
Seedlings that germinate on top of each other compete for the same water, light and root space. They come up thin and spindly, they are far more vulnerable to damping off disease, and a good proportion of them die. You end up with a weaker stand than if you had seeded at the correct rate, and you paid twice for it.
Stick to the published rate. If you want a denser lawn, the answer is soil preparation and consistent watering during establishment, not more seed.
Timing decides whether any of this works
Seed timing matters more than almost anything else, and the right window depends entirely on whether your grass is cool season or warm season.
Cool season grasses (fescues, bluegrass, ryegrass) want late summer into early fall. Mid August through late September across most of the northern US. Soil is still warm enough for fast germination, air is cooling, weed pressure has dropped off, and the new grass gets fall plus spring to establish before it faces a summer. Spring seeding is the backup option and it is distinctly worse, because the lawn hits summer heat with a three month old root system and crabgrass competes the whole way.
Warm season grasses (bermuda, zoysia, centipede, bahia) want late spring into early summer, once soil temperature is reliably above 65F and ideally closer to 70F. Seeding these in fall is close to wasted money, because they germinate and then go dormant before rooting properly, and winter kills a large share of them.
Overseeding versus starting over
Overseeding is spreading seed into an existing lawn to thicken it. The rate is roughly half the new lawn rate, because you already have grass covering part of the ground.
The thing that determines whether overseeding works is seed to soil contact. Seed sitting on top of thatch or existing turf will not germinate reliably, it dries out and birds take it. Core aerate first, or rent a slit seeder which cuts grooves and drops seed directly into them. Broadcasting seed onto an unprepared lawn gives you maybe 20 percent germination and mostly wasted seed.
If more than about half the lawn is bare or weeds, overseeding is not the right tool. Kill it off, prepare the soil properly and start fresh at the full new lawn rate.
What it costs
Quality seed runs $3 to $6 per pound for common fescue and ryegrass blends, more for elite bluegrass cultivars and considerably more for zoysia. A 50 pound bag of decent tall fescue runs $100 to $160.
For a 5,000 square foot lawn seeded new with tall fescue at 8 pounds per 1,000, that is 40 pounds, so roughly one bag and somewhere near $120. Overseeding the same lawn takes 20 pounds, so about $60.
Buy seed by the cultivar name rather than the marketing name on the front of the bag. Check the label for weed seed and other crop percentages. Cheap seed is cheap because it contains filler, annual ryegrass that dies after one season, and enough weed seed to matter.
Common questions
How much grass seed do I need for 1,000 square feet?
It depends on the species. Tall fescue and perennial ryegrass need about 8 pounds for a new lawn, Kentucky bluegrass and bermuda need about 2 pounds, and centipede needs only half a pound. Overseeding rates are roughly half the new lawn rate.
Can you put down too much grass seed?
Yes, and it backfires. Seedlings crowded together compete for water and light, grow thin and spindly, and are much more prone to damping off disease. Overseeding heavier gives you a weaker lawn than the correct rate, not a thicker one.
When is the best time to plant grass seed?
For cool season grasses such as fescue and bluegrass, late summer into early fall, roughly mid August to late September in the northern US. For warm season grasses such as bermuda and zoysia, late spring into early summer once soil temperatures are above 65F.
How much seed do I need to overseed an existing lawn?
About half the new lawn rate. For tall fescue that is 4 pounds per 1,000 square feet instead of 8. Aerate or slit seed first, because seed that does not reach soil will not germinate reliably.
How long does grass seed take to germinate?
Perennial ryegrass is fastest at 5 to 7 days. Tall fescue takes 7 to 14 days, Kentucky bluegrass 14 to 21, and bermuda 10 to 21 in warm soil. Keep the surface consistently damp through the whole window or germination stalls.
These figures are planning estimates. Bulk material weight shifts with moisture and screen size, and suppliers round differently, so confirm the final quantity with your yard before you order.