Grass Seed Calculator
Work out how much grass seed a lawn needs — area, grass type, new lawn or overseeding, kilos or pounds, bags to buy and cost.
Lawn size
Seed
Enter the lawn size — the seed estimate updates as you type.
- Grass seed needed
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- Bags to buy
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- Lawn area to seed
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- Seeding rate
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- Left over
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- One bag covers
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- Estimated cost
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An estimate, not a guarantee. Seeding rates vary between seed houses, cultivars and climates, so check the rate printed on the bag and use it instead of the preset if it differs. Sowing much heavier than the recommended rate does not give a thicker lawn — the seedlings compete with each other and thin out.
How it works
The calculator uses the standard sowing formula:
seed = lawn area × seeding rate. Rates are held internally in grams per square
metre and converted with 1 g/m² = 0.2048 lb per 1,000 sq ft (1,000 sq ft is
92.903 m², and a pound is 453.592 g). So a 10 × 8 m lawn is 80 m², and at the usual
new-lawn rate for a perennial ryegrass mix of 35 g/m² that is 2,800 g — 2.80 kg, or one 5 kg
bag with 2.2 kg to spare. In imperial the same lawn is 861 sq ft at 7.17 lb per 1,000 sq ft,
which is 6.17 lb.
Presets follow the common trade recommendations: about 35 g/m² (7 lb per 1,000 sq ft) for ryegrass and tall fescue on bare soil, 25 g/m² for fine fescues, 15 g/m² for Kentucky bluegrass, and only 5 g/m² for the tiny seeds of Bermudagrass and zoysia. Overseeding an existing lawn uses roughly two-thirds of the new-lawn rate, and patch repair uses one and a half times it, because bare scars need to fill fast. Pick a grass and a job and the rate fills in; type over it at any time and the grass selector switches to “Custom rate”.
Bags are always rounded up — you cannot buy 0.56 of a bag — and the leftover figure tells you how much is spare for repairs next season. Everything is plain arithmetic run in your browser: your measurements are never uploaded, stored or sent anywhere, and there are no ads or sign-ups.
Frequently asked questions
How much grass seed do I need?
Multiply the area you are seeding by the sowing rate. A 10 × 8 m lawn is 80 m², and at the usual new-lawn rate for a perennial ryegrass mix of 35 g/m² that is 2,800 g — 2.80 kg, or one 5 kg bag with 2.2 kg to spare. In imperial the same lawn is 861 sq ft at about 7.2 lb per 1,000 sq ft, which is 6.17 lb. Rates differ by grass: fine fescues want about 25 g/m², Kentucky bluegrass 15 g/m², and the very small seeds of Bermudagrass and zoysia only 5 g/m².
What is the difference between the seeding rate for a new lawn and for overseeding?
Overseeding an existing lawn uses roughly two-thirds of the new-lawn rate — around 25 g/m² (5 lb per 1,000 sq ft) for a ryegrass or fescue mix — because the established turf is already covering the ground and the new seed is only filling gaps. Bare soil gets the full rate, and patch repair on a worn scar gets about one and a half times it so the bare ground closes quickly. Pick the job in the calculator and the rate changes for you.
Can I just sow extra grass seed to get a thicker lawn?
No — sowing much heavier than the recommended rate backfires. The seedlings germinate on top of each other, compete for light, water and nutrients, and thin out or turn spindly and disease-prone. A modest 10–15% margin for wind, birds and edges is sensible; double the rate is wasted money. If the bag lists its own sowing rate, type that into the rate field instead of the preset, since it is matched to that exact cultivar blend.