Calculate how much grass seed you need for a new lawn or overseeding based on your lawn size and grass type, plus bags to buy and estimated cost.
Grass Seed Formula
The amount of seed you need depends on your lawn area and the seeding rate for your grass type. To find pounds of seed:
S = A / 1000 * R
To find how much area a fixed amount of seed will cover, rearrange the formula:
A = S / R * 1000
- S = seed needed, in pounds (lbs)
- A = lawn area, in square feet
- R = seeding rate, in pounds per 1,000 square feet
The seeding rate (R) is the key value. It changes with the grass type because seed size differs between species, and it changes with the project, product, region and lawn condition. The calculator presets are illustrative planning assumptions; use the rate on your seed bag rather than assuming overseeding always uses half the new-lawn rate. The calculator divides your area by 1,000 to get the number of "thousand square foot" units, then multiplies by the rate to get total pounds. If you enter a bag size, it rounds up to whole bags. A price per pound gives a seed-used estimate and, with bag size, a separate whole-bag purchase estimate; taxes and delivery are omitted.
Seeding Rates by Grass Type
These are illustrative planning ranges in pounds per 1,000 square feet, not universal application recommendations. Product and regional directions may differ. Use the seed-bag rate for the selected project; the calculator rate is editable.
| Grass Type | New Lawn (lbs/1,000 sq ft) | Overseeding (lbs/1,000 sq ft) |
|---|---|---|
| Tall fescue | 8 to 10 | 4 to 6 |
| Kentucky bluegrass | 2 to 3 | 1 to 2 |
| Perennial ryegrass | 7 to 9 | 3 to 4 |
| Fine fescue | 4 to 5 | 3 to 4 |
| Bermudagrass | 1 to 2 | 1 |
| Zoysiagrass | 1 to 2 | 1 |
| Centipedegrass | 0.25 to 0.5 | 0.25 |
Example Problems
Example 1: New tall fescue lawn. You are seeding a bare yard that measures 50 feet by 60 feet, so the area is 3,000 square feet. Tall fescue for a new lawn uses about 9 lbs per 1,000 square feet. Divide 3,000 by 1,000 to get 3, then multiply by 9. You need about 27 pounds of seed. If you buy 20 lb bags, that is 2 bags.
Example 2: Overseeding Kentucky bluegrass. You want to thicken an existing 5,000 square foot bluegrass lawn. The overseeding rate is about 1.5 lbs per 1,000 square feet. Divide 5,000 by 1,000 to get 5, then multiply by 1.5. You need about 7.5 pounds of seed.
Frequently Asked Questions
How much grass seed do I need per square foot? Most lawns use between 0.001 and 0.01 pounds per square foot, which is easier to read as pounds per 1,000 square feet. Tall fescue runs about 8 to 10 lbs per 1,000 square feet for a new lawn, while fine-seeded grasses like Kentucky bluegrass use only 2 to 3 lbs over the same area. Match the rate to your grass type rather than guessing per square foot.
Why is the overseeding rate lower than the new lawn rate? Overseeding adds seed to a lawn that already has living grass, so you only need enough new seedlings to fill gaps and thicken the stand. A new lawn starts from bare soil and needs the full rate to form complete cover. The appropriate rate depends on the product and existing stand; do not assume a universal half-rate.
Should I buy extra seed? Yes. Buying about 5 to 10 percent more than the calculated amount covers edges, bare spots, and uneven spreading. Seed stored in a cool, dry place stays viable for a season, so a small surplus is not wasted.
