How this calculator works
Grass seed is sown by weight per square metre. The usual rate is about 35 grams per m² for a new lawn (roughly an ounce per square yard), more for a hard-wearing or shady mix, and less for overseeding a thin lawn. Multiply the area by the rate, then add an allowance for uneven spreading and losses.
Worked example: a 6 × 5 m lawn (30 m²) sown at 35 g per m² with 10% extra needs 30 × 35 × 1.1 = 1,155 g, which is 1.16 kg. Buy two 1 kg boxes, or one 5 kg box.
Seed for common lawn sizes at 35 g per m² (10% extra)
New lawn. Use the other rates for overseeding or shady mixes.
| Lawn | Area | Seed | 1 kg boxes |
|---|---|---|---|
| 4 × 3 m | 12 m² | 0.46 kg | 1 |
| 5 × 4 m | 20 m² | 0.77 kg | 1 |
| 6 × 5 m | 30 m² | 1.16 kg | 2 |
| 8 × 5 m | 40 m² | 1.54 kg | 2 |
| 10 × 6 m | 60 m² | 2.31 kg | 3 |
| 10 × 8 m | 80 m² | 3.08 kg | 4 |
Tips before you buy
- Prepare the ground as you would for turf: clear weeds and stones, dig it over, level it, firm it by treading and rake it to a fine tilth. Rake in a pre-seeding fertiliser a few days before.
- Sow in early autumn or spring, when the soil is warm and damp. The grass germinates in one to three weeks, depending on the temperature.
- Keep it moist, but not soaking, until the grass is established, and do not mow until it is about 6 to 8 cm tall. Then take off no more than a third.
- Use a mix that suits the place: a hard-wearing mix with ryegrass for family lawns, and a shade mix under trees.
- Cover the seed with a light raking, and protect it from birds with netting or by scaring them, if you can.
Tools & materials for this project
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Frequently asked questions
How much grass seed do I need for a 30 m² lawn?
About 1.2 kg for a new lawn at 35 g per m² with 10% extra. Buy two 1 kg boxes.
How much seed per m² for overseeding?
About 15 to 20 g per m², so a 30 m² lawn needs 0.5 to 0.7 kg.
How many m² does 1 kg of grass seed cover?
About 29 m² at 35 g per m² for a new lawn, 50 m² at 20 g per m² when overseeding.
When is the best time to sow grass seed?
Early autumn is best, while the soil is still warm and the rain returns. Spring sowing also works, but needs more watering and more weeding.
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