Garden & outdoor
How much grass seed do you need for your lawn?
Kilograms of grass seed and starter fertilizer for a new lawn or overseeding, based on your lawn area.
Quick answer
Most failed lawns die in the first three weeks, and the two classic causes are sowing too thin — gaps that weeds immediately colonize — and sowing too thick, where seedlings choke each other competing for light and water. The standard rates for cool-season mixes (perennial ryegrass, fescue, Kentucky bluegrass) are about 35 g/m² for a brand-new lawn and roughly half that, 18 g/m², when overseeding an existing one.
Grass seed needed
3.5 kg
- In 1 kg boxes
- 4 boxes
- Starter fertilizer
- 3 kg
Rates for typical cool-season mixes (ryegrass, fescue, bluegrass): ~35 g/m² for new lawns, ~18 g/m² for overseeding. Starter fertilizer at ~30 g/m² helps germination. Sow in early autumn or spring, keep the soil moist for 2-3 weeks, and don’t mow until blades pass 8-10 cm.
How it works
The calculator converts your area into kilograms of seed and starter fertilizer, which is the other half of the job: a phosphorus-rich starter at ~30 g/m² feeds root development during germination. Timing matters more than any product — early autumn is ideal in most climates (warm soil, cool air, fewer weeds), spring is the runner-up. After sowing, the only rule that counts: keep the top centimetre of soil constantly moist until germination, which can mean watering lightly once or twice a day for 2-3 weeks.
Frequently asked questions
How much grass seed do I need for 100 m²?+
About 3.5 kg for a new lawn at the standard 35 g/m² rate, or roughly 1.8 kg for overseeding. Buy about 10% extra for edge losses and touch-ups of spots that germinate poorly — practically, a 4 kg box covers a 100 m² new lawn comfortably.
When is the best time to sow a lawn?+
Early autumn (September to mid-October in temperate climates) is best: the soil is still warm so germination is fast, the air is cooler so seedlings don’t scorch, and annual weeds are winding down. Spring (April-May) works too but you’ll fight more weeds and must water through the first summer. Avoid mid-summer sowing entirely.
When can I mow a newly seeded lawn?+
When the blades reach 8-10 cm, usually 4-6 weeks after germination, cut down to about 6 cm — never remove more than a third of the height in one pass. Make sure the mower blades are sharp and the soil is dry, or you’ll uproot seedlings. After 2-3 gentle cuts the young lawn can be treated normally.
Why did my grass seed not germinate?+
The usual suspects, in order: the soil dried out between waterings (the number one killer), seed buried too deep (it should sit in the top 0.5-1 cm, lightly raked in), soil temperature below 10 °C, or old seed stored badly. Birds and heavy rain washing seed away account for most of the rest — a light covering of soil or straw prevents both.
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