How to calculate grass seed
Grass seed is sold and applied by a seeding rate — a weight of seed per unit area, almost always expressed in pounds per 1,000 square feet. To find the total you need, multiply your area by the rate and divide by 1,000:
Seed needed (lbs) = Area (sq ft) × Seeding rate (lbs per 1,000 sq ft) ÷ 1,000
For example, a 5,000 sq ft lawn seeded at 6 lbs per 1,000 sq ft needs 5,000 × 6 ÷ 1,000 = 30 lbs of seed. If you are overseeding an existing lawn rather than starting from bare soil, use about half the rate, since the established turf already covers much of the ground.
Why the seeding rate matters
The rate is not arbitrary — it is set so that seeds land close enough to form a dense, uniform stand without crowding each other. Seed too lightly and you get thin, patchy turf that invites weeds; seed too heavily and the young seedlings compete for water, light, and nutrients, producing weak grass prone to disease. Seed producers publish a recommended rate on the bag for each species and blend, and that number is your best starting point.
Typical seeding rates by grass type
Rates vary widely by species because seed size and growth habit differ. Common new-lawn rates (pounds per 1,000 sq ft):
- Kentucky bluegrass: 2–3 lbs (tiny seeds, ~1–2 million seeds per lb, spreads by rhizomes).
- Perennial ryegrass: 5–9 lbs (larger seeds, fast germination).
- Tall fescue: 6–10 lbs (bunch-type, needs a higher rate for density).
- Fine fescue: 3–5 lbs (fine texture, shade tolerant).
- Bermudagrass (hulled): 1–2 lbs (very small seed, warm-season).
Overseeding an existing lawn typically uses roughly half these amounts.
Useful area conversions
- 1 acre = 43,560 sq ft, so an acre at 6 lbs per 1,000 sq ft needs about 261 lbs of seed.
- A rectangular area is length × width in feet; a circle is π × radius².
- Subtract driveways, beds, and buildings from your measured area so you do not over-buy.