Grass Seed Calculator
Calculate how much grass seed you need for a new lawn or overseeding an existing one.
Covers all major grass types with correct seeding rates.
Why Seeding Rates Vary So Much Grass seed rates vary enormously by species — getting this wrong wastes money or leaves a patchy, thin lawn. The difference comes down to seed size: Kentucky Bluegrass has tiny seeds (approximately 2 million seeds per pound), so a small weight covers a large area. Tall Fescue has much larger seeds (around 450,000 per pound) and requires significantly more by weight. Always follow the recommended rate for your specific grass type.
Cool-Season vs. Warm-Season Grasses This is the most important choice for new lawn installation. Cool-season grasses (Kentucky Bluegrass, Tall Fescue, Fine Fescue, Perennial Ryegrass) thrive in the northern US (roughly north of a line from Washington DC to Kansas City to San Francisco). They grow actively in spring and fall, go semi-dormant in summer heat, and should be seeded in late summer or early fall when soil temperatures are 50–65°F. Warm-season grasses (Bermuda, Zoysia, Centipede, St. Augustine) thrive in the South and only grow when soil temperatures exceed 65–70°F. They go dormant and turn brown in winter and should be seeded in late spring.
New Lawn vs. Overseeding A new lawn on bare soil requires a full seeding rate to establish thick, competitive coverage from scratch. Overseeding — adding seed to an existing lawn to thicken it or repair bare spots — uses roughly half the new-lawn rate, since existing grass provides competition and you don’t need to cover every square inch from zero.
Proper Soil Preparation The most common reason for seeding failure is poor seed-to-soil contact. Till bare soil 2–3 inches deep, break up clumps, remove rocks and debris, and add starter fertilizer before seeding. After spreading seed, lightly rake it into the top ¼ inch of soil. Straw mulch helps retain moisture but should be thin enough that you can still see 50% of the soil surface.
Germination Times by Grass Type Perennial Ryegrass germinates fastest — 7 days under good conditions. Tall Fescue takes 10–14 days. Kentucky Bluegrass is the slowest at 14–21 days and requires patience. Zoysia is notoriously slow at 14–21 days or longer. Keep soil consistently moist until germination — let it dry out once and you may lose the entire seeding.