Grass seed calculator

Seeding rates vary a lot by grass type — a bluegrass lawn uses a fraction of the seed a tall fescue lawn does. The rates here are typical midpoints from extension guides.

How the seed calculation works

Seed labels and extension services give seeding rates in pounds of seed per 1,000 sq ft. Divide your lawn area by 1,000 and multiply by the rate.

pounds of seed = area (sq ft) ÷ 1,000 × rate (lb per 1,000 sq ft)
metric: grams = area (m²) × rate (g per m²)
1 lb per 1,000 sq ft ≈ 4.9 g per m² · 1 acre = 43,560 sq ft

Worked examples: how much grass seed for 1,000 sq ft of tall fescue, how much Kentucky bluegrass seed for 5,000 sq ft, how much grass seed for a 1/4 acre, how much seed to overseed 5,000 sq ft and, in metric, how much grass seed for 100 m².

Typical seeding rates

Seed size explains most of the difference. A pound of Kentucky bluegrass contains several times as many seeds as a pound of tall fescue — commonly quoted as five to ten times, so the same coverage takes far fewer pounds.

Winter overseeding a bermuda lawn

Bermuda goes brown after the first frosts. Seeding ryegrass into it in fall gives a green lawn until spring, and it takes far more seed than ordinary overseeding: University of Tennessee Extension (W161-J) puts the first overseeding at 10–15 lb or more per 1,000 sq ft, and the University of Arizona (AZ1683) uses 12–15 lb. Clemson’s Home & Garden Information Center is lighter-handed, suggesting about 5 lb on an established lawn so the ryegrass doesn’t fight the bermuda as it greens up in spring, and 10 lb on bare ground. The calculator uses 10 lb for perennial ryegrass and 12 lb for annual ryegrass; pick "Rate from my seed bag" to follow the product instead.

Mow the bermuda lower than usual and clear the clippings first so the seed reaches the soil, but don’t scalp it to the dirt. Clemson times it about 30 days before the first frost. Don’t do this to centipede, St. Augustine or zoysia lawns: all three sources warn against it, and Clemson says the ryegrass can severely set them back in spring.

Adjusting for seed quality (pure live seed)

The label lists purity (how much of the bag is the seed you want) and germination (how much of that seed sprouts in a lab test). Multiply them to get the pure live seed (PLS) fraction, then divide the rate by it — the method LSU AgCenter and Penn State Extension both teach. Put the two label numbers in More options and the calculator does it for you.

bag weight rate = PLS rate ÷ (purity × germination)
6 lb ÷ (0.90 × 0.85) = 7.8 lb of seed from the bag

Seed at 90% purity and 85% germination is about 77% pure live seed, so a 6 lb rate becomes nearly 8 lb of that product. A cheap bag can end up costing more per live seed than a better one.

Coated seed carries a clay, fertilizer or moisture coating that can be half the weight in the bag, and the label must show the coating percentage (UConn Extension’s guide to seed labels walks through one at 50%). If the bag gives its own seeding rate, use it; otherwise pick the coating level in More options, or enter the label’s purity, which on coated seed already leaves the coating out.

Straw and starter fertilizer for new seed

On bare soil, a thin layer of weed-free straw keeps the seed damp and stops it washing off slopes. UNH Extension suggests about one bale per 1,000 sq ft and Rutgers 50–90 lb (1–2 bales); the calculator shows 1–1.5 bales. Use straw, not hay, which is full of seed heads.

A starter fertilizer helps new roots. The UC Guide to Healthy Lawns suggests at least 1 lb of phosphorus per 1,000 sq ft at planting but no more than 1 lb of nitrogen; UMass, working from soil tests, lists as little as 0.5 lb phosphate for new lawns. A soil test is the real answer. The calculator shows a 24-25-4 starter at 4 lb per 1,000 sq ft, which supplies about 1 lb each of phosphate and nitrogen; for other analyses use the lawn fertilizer calculator.

Tips for better germination

• Rake or core-aerate first so seed touches soil. Seed sitting on thatch mostly feeds birds.
• Split the seed in two and spread half in one direction and half at right angles.
• Keep the top half-inch of soil moist until seedlings are up — often light watering once or twice a day. The garden watering calculator turns that into gallons and minutes.
• Check the label for weed seed and "other crop" percentages, and the test date.
• Hold off on weed-and-feed and crabgrass preventers around seeding time; most stop grass seed too. Use only a product labeled for newly seeded lawns (Rutgers, UNH Extension).

Measure first with the lawn area calculator. Deciding between seed and sod? Read overseeding vs sod, or compare with how much sod for 1,000 sq ft.

New to the words on a seed bag — overseeding, pure live seed, coated seed? They are explained in plain English in words you’ll hear at the yard.