Grass Seed Calculator
Find out how much grass seed to buy for a new lawn or for overseeding a thin one. Pick your grass type and enter the size of your lawn, and this grass seed calculator shows the pounds of seed you need and how many bags to buy, using seeding rates published by university extension services.
Your results will appear here.
How to use the grass seed calculator
- Measure the lawn. Enter the length and width, a circle diameter, or the total area. Leave out the house, driveway, patios and planting beds.
- Choose your grass type. If you are buying a mix, choose “Other” and enter the new-lawn rate printed on the bag.
- Choose the project. A new lawn on bare soil uses the full rate. Overseeding an existing lawn uses about half.
- Pick a bag size and enter the price per bag to see the cost.
Grass seed formula
Seed (lb) = Lawn area (sq ft) ÷ 1,000 × Seeding rate (lb per 1,000 sq ft)
Overseeding: use about half the new-lawn rate
Bags = Seed (lb) ÷ Bag size (lb), rounded up
Worked example
A new tall fescue lawn measures 50 ft by 40 ft, and the seed comes in 7 lb bags:
- Area: 50 × 40 = 2,000 sq ft, which is 2 “thousands”
- Seed: 2 × 7 lb = 14 lb, up to 2 × 9 lb = 18 lb, so 14 to 18 lb
- Bags: 18 ÷ 7 = 2.6, rounded up to 3 bags
Overseeding a 5,000 sq ft Kentucky bluegrass lawn at half of the 1 to 2 lb rate needs only 2.5 to 5 lb of seed.
Seeding rates by grass type
| Grass | Season | New lawn (lb per 1,000 sq ft) | Overseeding (about half) |
|---|---|---|---|
| Tall fescue | Cool | 7 – 9 | 3.5 – 4.5 |
| Perennial ryegrass | Cool | 7 – 9 | 3.5 – 4.5 |
| Fine fescue (red, chewings, hard) | Cool | 4 – 6 | 2 – 3 |
| Kentucky bluegrass | Cool | 1 – 2 | 0.5 – 1 |
| Bahiagrass | Warm | 8 – 10 | 4 – 5 |
| Bermudagrass (hulled) | Warm | 1 – 2 | 0.5 – 1 |
| Zoysiagrass | Warm | 1 – 2 | 0.5 – 1 |
| Centipedegrass | Warm | 0.25 – 0.5 | 0.13 – 0.25 |
Cool-season rates follow UMass Extension’s seeding table. Warm-season rates come from the North Carolina Department of Agriculture and UF/IFAS Extension. Rates differ so much because seed size differs: a pound of Kentucky bluegrass holds far more seeds than a pound of tall fescue.
Tips for seeding a lawn
- Seed at the right time. Cool-season grasses do best when seeded in late summer or early fall. Warm-season grasses do best in late spring and early summer, once the soil is warm.
- Read the label. Seed mixes and coated seed have their own rates. Use the rate on your bag when it is different from the table.
- Do not double the rate. Seeding much heavier than recommended crowds the seedlings and can make the new grass weaker, not thicker.
- Split it in two passes. Spread half the seed walking in one direction and half walking across it for even coverage.
- Keep the seed moist. Water lightly and often until the grass is up. Kentucky bluegrass can take two to four weeks to sprout.
Frequently asked questions
How much grass seed do I need per 1,000 square feet?
It depends on the grass. A new lawn needs about 7 to 9 lb of tall fescue or perennial ryegrass, 4 to 6 lb of fine fescue, 1 to 2 lb of Kentucky bluegrass, Bermudagrass or zoysia, and only 0.25 to 0.5 lb of centipedegrass.
How much seed do I need to overseed?
Overseeding an existing lawn usually takes about half the new-lawn rate, because you are filling thin spots rather than seeding bare soil.
How much grass seed do I need for an acre?
An acre is 43,560 sq ft, or 43.56 thousand square feet. Multiply that by the rate. For tall fescue at 7 to 9 lb per 1,000 sq ft, that is about 305 to 392 lb.
Can I put down too much grass seed?
Yes. Too much seed makes the seedlings compete for water, light and nutrients, which can lead to thin, weak turf. Stay close to the recommended rate.
Why does my seed bag show a different rate?
Bag rates are set for that exact mix, coating and seed quality, so they can differ from general tables. When the two differ, follow the bag.
Sources and methodology
The formulas on this page were written and checked by the HomeQuantly Team against the worked examples shown above. Results are estimates for planning; always confirm measurements on site before you buy materials.