How to use the grass seed calculator
- Measure the lawn and enter length × width, or the total area if you already know it. For odd shapes, split the yard into rectangles and add them up.
- Choose your grass type. Each one loads a typical new-lawn seeding rate in pounds per 1,000 sq ft. If your seed bag lists a different rate, type it in.
- Choose the job. A new lawn on bare soil uses the full rate; overseeding a thin lawn uses roughly half.
- Pick a bag size to see how many bags to buy.
The grass seed formula
Pounds of seed = area (sq ft) ÷ 1,000 × seeding rate (lb per 1,000 sq ft)
Seeding rates are always given per 1,000 square feet because that is how university turfgrass programs publish them. Seed size drives the rate: Kentucky bluegrass seed is tiny, so a couple of pounds covers 1,000 sq ft, while tall fescue seed is large and needs several times more by weight.
Seeding rates by grass type (new lawns)
Ranges from Virginia Tech's turfgrass establishment guide (Virginia Cooperative Extension), with Ohio State and Illinois Extension figures where they differ; the calculator uses a value inside each range:
- Tall fescue: 6–8 lb (Ohio State lists 8–10)
- Kentucky bluegrass: 2–3 lb
- Perennial ryegrass: 3–5 lb (Ohio State lists 7–8)
- Fine fescues: 3–5 lb
- Bluegrass/ryegrass mix (80:20): 3–4 lb; bluegrass/fine fescue (50:50): 3–5 lb (Illinois Extension)
- Bermudagrass: 1–2 lb hulled, 5–10 lb unhulled
- Zoysiagrass: 1–2 lb; centipedegrass: 0.25–0.5 lb
Extension specialists warn that seeding heavier than recommended produces crowded, weak seedlings that are more prone to disease, so more seed is not better.
Worked example
A new 100 × 50 ft lawn of tall fescue at 7 lb per 1,000 sq ft:
- Area: 100 × 50 = 5,000 sq ft
- Seed: 5,000 ÷ 1,000 × 7 = 35 lb (15.9 kg)
- Bags: 35 ÷ 20 = 1.75, so 2 bags of 20 lb, or 5 bags of 7 lb
Overseeding the same lawn at half rate takes about 17.5 lb.
Overseeding vs. a new lawn
A common rule of thumb is to overseed an existing, thin lawn at about half the new-lawn rate; always check the overseeding rate printed on your seed label. Mow short, rake or core aerate first so seed reaches the soil, and topdress with about 1/4 inch of compost if you like; the compost calculator works out how much.
Tips for good germination
- Seed at the right time. Cool-season grasses (fescue, bluegrass, ryegrass) do best seeded in late summer to early fall; warm-season grasses (bermuda, zoysia, centipede) in late spring and early summer.
- Split the seed in half and spread it in two passes at right angles for even coverage, as Illinois Extension suggests.
- Rake lightly to cover seed with about 1/8 to 1/4 inch of soil, then roll for good seed-to-soil contact.
- Keep the top half inch moist with light, frequent watering until the grass is established.
- Filling low spots first? The topsoil calculator gives cubic yards for a few inches of new soil.
Frequently asked questions
How much grass seed do I need per 1,000 square feet?
It depends on the grass: about 6–8 lb of tall fescue, 2–3 lb of Kentucky bluegrass, 3–5 lb of perennial ryegrass or fine fescue, and 1–2 lb of hulled bermudagrass for a new lawn.
How much grass seed do I need for an acre?
An acre is 43,560 sq ft, or 43.56 thousand square feet. At 7 lb per 1,000 sq ft, tall fescue takes about 305 lb per acre; Kentucky bluegrass at 2.5 lb takes about 109 lb.
How much grass seed do I need to overseed?
A common rule of thumb is about half the new-lawn rate, for example 3–4 lb of tall fescue per 1,000 sq ft. Follow the overseeding rate on the seed label when one is given.
How many square feet does a 50 lb bag of grass seed cover?
At 7 lb per 1,000 sq ft, 50 lb of tall fescue covers about 7,100 sq ft as a new lawn. The same bag of Kentucky bluegrass at 2.5 lb covers about 20,000 sq ft.
Can I put down too much grass seed?
Yes. Seeding far above the recommended rate creates crowded, weak seedlings that compete with each other and are more prone to disease.