Lawn Overseeding Calculator

Lawn Overseeding is the process of spreading grass seed over an existing lawn to fill in thin or bare spots, improve density, and introduce improved grass varieties. The amount of seed needed depends on the lawn area, grass type, and whether you are overseeding or establishing a new lawn.

The Formula: Seed Needed (lbs) = Lawn Area (sq ft) × Seeding Rate (lbs per 1,000 sq ft) / 1,000

Overseeding vs New Lawn Rates: Overseeding uses about half the rate of new lawn establishment because existing turf already covers much of the ground.

Seeding Rates by Grass Type (per 1,000 sq ft / per 93 sq m): Cool-season grasses:

• Kentucky Bluegrass: New lawn 2 lbs (0.9 kg), Overseed 1 lb (0.45 kg)
• Perennial Ryegrass: New lawn 8 lbs (3.6 kg), Overseed 4 lbs (1.8 kg)
• Tall Fescue: New lawn 8 lbs (3.6 kg), Overseed 4 lbs (1.8 kg)
• Fine Fescue: New lawn 4 lbs (1.8 kg), Overseed 2 lbs (0.9 kg)

Warm-season grasses:

• Bermuda Grass (hulled): New lawn 1 lb (0.45 kg), Overseed 0.5 lb (0.23 kg)
• Zoysia Grass: New lawn 2 lbs (0.9 kg), Overseed 1 lb (0.45 kg)

Bermuda catches people out. Its seed is tiny, close to 1.8 million to the pound, so a single pound covers 1,000 sq ft at a sensible density. Sow it at the fescue rate and you get a matted, disease-prone stand that thins itself out over the first season.

Timing Matters: Cool-season grasses are best overseeded in early fall (September in the Northern Hemisphere) when soil temperatures are 50 to 65°F (10 to 18°C). Warm-season grasses should be overseeded in late spring when soil temperatures reach 65 to 70°F (18 to 21°C).

Practical Tips: Mow your existing lawn short (about 2 inches / 5 cm) before overseeding to let seed reach the soil. Aerate the lawn before overseeding for best seed-to-soil contact. Keep the seeded area consistently moist for 2 to 3 weeks until germination. Add about 10 to 15 percent extra seed to account for losses from wind, birds, and poor germination.

Coverage Estimation: A 5-pound (2.3 kg) bag of tall fescue covers a little over 1,000 sq ft (93 sq m) for overseeding, once you allow the usual 10% for spreader spill and edges. A typical suburban lawn of 5,000 sq ft (465 sq m) works out at about 22 pounds (10 kg) of tall fescue for overseeding, or 44 pounds (20 kg) to start one from bare soil.

One thing that quietly kills an overseeding: Crabgrass pre-emergent. It works by stopping seeds from germinating, and it has no way to tell a weed seed from the grass seed you just paid for. Applying both in the same season wastes the seed entirely. If you have already put pre-emergent down this spring, wait for the fall window instead. The exception is siduron, sold as Tupersan, which is the one pre-emergent that lets grass seed through.