Lawn Seed Calculator
Work out how much grass seed a lawn needs — from the area and your product's own coverage, for a new lawn or for overseeding.
Grass seed is not one-size-fits-all: every product states its own coverage, and a new lawn needs twice the seed of an overseed. This calculator uses your product's figure and your job type.
For instant grass, compare with the sod calculator.
Your results
Enter your measurements and press Calculate.
Quantities are rounded up to whole tiles, planks, boxes or bags, after the wastage allowance. Cost appears only when you enter a price.
Formula
All lengths are converted to a single unit before the calculation: 1 ft = 0.3048 m, 1 in = 25.4 mm, 1 ft² = 0.09290304 m², 1 yd² = 9 ft². Material quantities are rounded up — you cannot buy part of a tile, plank or bag.
How to use this calculator
- Choose the shape of the lawn area.
- Choose new lawn or overseeding (overseeding uses half the seed).
- Enter the coverage from the seed packaging.
- Add a bag size or price if you want a bag count or cost.
Worked example
| Lawn | 50 ft × 20 ft = 1,000 ft² |
|---|---|
| Coverage | 500 ft² per lb |
| New lawn | 1,000 ÷ 500 = 2 lb (0.91 kg) |
| Overseeding | 2 × 0.5 = 1 lb (0.45 kg) |
Check it by hand: every step above uses the formula in the box. If your numbers match the example inputs but the calculator gives a different answer, please report it via the contact page.
Frequently asked questions
How much grass seed do I need?
It depends on the product's coverage — typically 400–600 sq ft per lb (about 20 m² per kg) for a new lawn. Enter the coverage from the bag and this calculator does the rest. Overseeding uses half the rate.
What is the difference between new lawn and overseeding?
A new lawn is sown on bare soil at the full rate. Overseeding spreads seed over an existing lawn to thicken it, at half the rate — the existing grass fills the rest.
How much seed per square metre?
About 25–50 g per m² for a new lawn, depending on the grass type. That is the same as a coverage of 20–40 m² per kg — check your product's figure and enter it above.
When should I sow grass seed?
Spring or early autumn, when the soil is warm and moist. Avoid hot, dry spells — seed dries out before it germinates.
Related calculators
Estimates only. Results are for planning. Measure twice, confirm box coverage and tile sizes on the packaging you buy, and follow the manufacturer's instructions. See the disclaimer.