How to Calculate Grass Seed
Correct seeding rate is the difference between a thick healthy lawn and one with bare patches, washout stripes, or wasted seed. The amount needed depends on three factors: the grass species, whether you are establishing a new lawn or overseeding an existing one, and the total area in square feet or square meters. Every grass type has a recommended rate per 1,000 square feet because seed size and germination rate vary by species - 1 pound of bermuda grass contains 1.8 million seeds while 1 pound of Kentucky bluegrass contains over 2 million seeds.
Seed Rate Formula
The fundamental formula is area divided by 1,000, multiplied by the species-specific rate. For metric users, 1 pound per 1,000 sq ft equals approximately 4.88 grams per square meter:
Seeding Rates by Grass Type
Rates below are for PLS (pure live seed) from reputable suppliers. Bargain seed may include filler, weed seed, or chaff which lowers germination - always check the seed tag for germination percentage and pure seed content before comparing prices.
| Grass Type | Climate | New Lawn | Overseed | Germination |
|---|---|---|---|---|
| Kentucky Bluegrass | Cool | 2.5 lb/1000 | 1.5 lb/1000 | 14-30 days |
| Tall Fescue | Cool | 8 lb/1000 | 4 lb/1000 | 7-14 days |
| Perennial Ryegrass | Cool | 7 lb/1000 | 3.5 lb/1000 | 5-10 days |
| Fine Fescue | Cool (shade) | 4 lb/1000 | 2 lb/1000 | 7-14 days |
| Bermuda | Warm | 1 lb/1000 | 0.5 lb/1000 | 7-21 days |
| Zoysia | Warm | 2 lb/1000 | 1 lb/1000 | 14-21 days |
| Bahia | Warm | 8 lb/1000 | 4 lb/1000 | 14-28 days |
| Centipede | Warm (low-maint) | 0.5 lb/1000 | 0.25 lb/1000 | 14-21 days |
New Lawn vs. Overseeding vs. Repair
Why the rate differs between new lawn and overseeding:
- New lawn - uses the full rate because bare soil must be completely covered with seed to block incoming weed competition and provide even germination.
- Overseeding - uses half the rate since you are adding seed to an existing mature lawn. The existing turf already occupies most of the space; new seed just fills thin spots.
- Repair patches - use 25 percent more than new lawn rate because patch edges need heavier seeding to blend with surrounding grass.
Best Planting Windows
| Grass Type | Best Window | Soil Temp | Avoid |
|---|---|---|---|
| Cool-season | Late summer - early fall | 50-65 F (10-18 C) | Midsummer heat |
| Cool-season (backup) | Early spring | 50-60 F (10-15 C) | Late spring |
| Warm-season | Late spring - early summer | 65-70 F (18-21 C) | Fall (cannot establish) |
Planting Depth and Seed-to-Soil Contact
Grass seed needs to sit 1/8 to 1/4 inch (3-6 mm) below the soil surface. Deeper and seedlings cannot reach sunlight before using stored energy. Shallower and seeds dry out or wash away. Tall fescue can handle slightly deeper (up to 1/2 inch) while tiny seeds like bentgrass need to sit barely covered.
- Loosen top soil - rake the top 1/2 inch of soil to create a fine seedbed
- Spread seed - use a broadcast or drop spreader, never by hand
- Rake lightly - work seed into the top 1/4 inch of soil
- Compress - roll with a lawn roller or walk on plywood planks to press seed into contact with soil
- Straw cover - apply 1 bale per 1,000 sq ft to retain moisture and shade young seedlings
Watering Schedule During Germination
| Days After Seeding | Frequency | Amount |
|---|---|---|
| Days 1-14 | Twice daily (light) | Keep top 1/2 inch moist |
| Days 15-28 | Once daily | 1/4 inch water |
| Days 29-42 | Every other day | 1/2 inch water |
| Day 43+ | 2-3 times per week | 1 inch total per week |
First Mowing and Maintenance
Wait until new grass reaches 3 to 4 inches tall before the first mow, then cut only the top third (1 inch off). Mowing too early or too short damages young root systems before they have established. Skip fertilizer until the grass has been mowed 2-3 times - a starter fertilizer applied at seeding provides enough nutrients for the first 6 weeks.