Grass Seed Calculator
Calculate how many pounds of grass seed you need to overseed or establish a new lawn based on area and seeding rate.
How to use this tool
- Measure your lawn area in square feet (length × width).
- Check the seed bag label for the recommended seeding rate in lbs per 1,000 sq ft.
- Add a 10% waste factor for uneven spreading.
- The calculator shows base seed needed and total to purchase.
Find out exactly how much grass seed to buy before seeding or overseeding your lawn.
Formula
Base seed (lbs) = area (ft²) ÷ 1000 × seeding rate (lbs / 1000 ft²)
Total seed to buy (lbs) = base seed × (1 + waste % ÷ 100)
How it works
This calculator scales the manufacturer's recommended seeding rate (expressed per 1,000 square feet) to the actual lawn area, then adds a user-defined waste allowance to account for uneven spreading, edges, and seed lost to birds or wind.
Seeding rates differ between new lawn establishment (higher) and overseeding an existing lawn (lower); always use the rate specified on the seed bag for the intended application. The waste allowance of 5–15% is typical; steep slopes or irregular shapes may warrant a higher figure.
Worked example
Worked example
- Inputs: 2,000 ft² lawn, seeding rate 3 lbs per 1,000 ft², 10% waste allowance.
- Base seed = 2,000 ÷ 1,000 × 3 = 6.0 lbs.
- Total seed = 6.0 × (1 + 10 ÷ 100) = 6.0 × 1.10 = 6.6 lbs.
Base seed needed = 6.0 lbs; total seed to buy = 6.6 lbs.
Key terms
- Seeding rate
- The manufacturer-recommended weight of grass seed to apply per 1,000 square feet; varies by grass species and whether it is a new installation or overseeding.
- Overseeding
- Spreading seed over an existing lawn to fill thin patches and improve density, typically at half the new-lawn seeding rate.
- Waste allowance
- A percentage added to the base seed quantity to cover losses from spreading overlap, edges, wind drift, and bird feeding.
- Germination rate
- The percentage of seeds in a bag expected to sprout under good conditions; printed on the label and implicitly factored into the seeding rate recommendation.
Frequently asked questions
- How much grass seed do I need per square foot?
- Seeding rate is usually given per 1,000 sq ft. New lawns typically need 5–8 lbs/1,000 ft², while overseeding an existing lawn needs 3–4 lbs/1,000 ft².
- When is the best time to seed a lawn?
- Cool-season grasses (fescue, bluegrass, ryegrass) seed best in early fall or spring. Warm-season grasses (bermuda, zoysia) establish best from late spring to early summer.