How It Works
The calculator uses standard seeding rates published by university extension programs. The formula is straightforward:
Seed needed (lbs) = (Lawn area in sq ft / 1,000) x Seeding rate (lbs per 1,000 sq ft) x 1.10
The 1.10 multiplier adds a 10% buffer for uneven spreading, seed lost to wind, and areas that need a second pass. Every grass type has a different seeding rate — the calculator uses the midpoint of the recommended range.
Seeding Rates by Grass Type
| Grass Type | New Lawn (lbs/1,000 sq ft) | Overseed (lbs/1,000 sq ft) | Best Season | Climate |
|---|---|---|---|---|
| Kentucky Bluegrass | 2–3 | 1–2 | Early fall | Cool-season (Zones 2-7) |
| Perennial Ryegrass | 8–10 | 4–5 | Early fall | Cool-season (Zones 3-7) |
| Tall Fescue | 8–10 | 4–5 | Early fall | Cool / Transition (Zones 3-8) |
| Bermuda Grass | 1–2 | 0.5–1 | Late spring | Warm-season (Zones 7-10) |
| Fine Fescue | 4–5 | 2–3 | Early fall | Cool-season (Zones 2-7) |
| Zoysia | 1–2 | 0.5–1 | Late spring | Warm-season (Zones 6-11) |
New Lawn vs Overseeding: Which Do You Need?
New lawn seeding is for bare soil — starting from scratch after construction, removing an old lawn, or establishing grass where none existed. You need the full seeding rate because there is no existing turf to fill gaps.
Overseeding is for existing lawns that are thinning out, have bare patches, or need a thicker look. The rate is roughly half of new lawn seeding because existing grass already covers most of the ground. Overseed in fall for cool-season grasses and late spring for warm-season types.
Patching bare spots uses the full new-lawn rate but only over the damaged area. Measure just the bare patches, not your entire yard.
FAQ
When is the best time to plant grass seed?
For cool-season grasses (Kentucky Bluegrass, Fescue, Ryegrass), plant in early fall — September through mid-October in most regions. Soil is still warm enough for germination, but air temperatures are cooling down, reducing stress on seedlings. Spring (March-April) is a second option but carries more weed competition. For warm-season grasses (Bermuda, Zoysia), plant in late spring to early summer when soil temperatures consistently hit 65-70 F.
How long does grass seed take to germinate?
It depends on the type. Perennial Ryegrass is the fastest at 5-10 days. Tall Fescue and Fine Fescue take 7-14 days. Kentucky Bluegrass is slow — 14-30 days. Bermuda takes 10-30 days, and Zoysia is the slowest at 14-21 days. Keep the soil consistently moist (not soaked) during this period. Water lightly 2-3 times per day until seedlings are established.
Should I use starter fertilizer with grass seed?
Yes. Starter fertilizer is high in phosphorus, which promotes root development in new seedlings. Apply it at planting time according to the bag directions. Do not use regular lawn fertilizer — it is nitrogen-heavy and can burn young grass. A soil test beforehand helps you choose the right formula.
Grass seed vs sod: which is better?
Seed is 80-90% cheaper than sod and offers more variety options, but it takes 2-3 months to establish. Sod gives you an instant lawn but costs $0.30-0.80 per square foot for the material alone plus installation. For large areas, seed almost always wins on cost. For small patches, slopes prone to erosion, or impatient homeowners, sod is worth the premium.
Related Calculators
- Mulch Calculator — calculate mulch for top-dressing newly seeded areas
- Soil Volume Calculator — figure out how much topsoil to add before seeding