How much grass seed per m²?

For new lawns: general purpose 35g/m², fine/ornamental 25g/m², hard-wearing 40g/m², shade 30g/m². For overseeding, use half these rates.

When is the best time to sow grass seed?

September is ideal in the UK — soil is warm and autumn rain helps germination. Spring (March-May) is the second-best window.

How long does grass seed take to germinate?

Most grass seed germinates in 7-21 days depending on soil temperature. Fine fescues may take longer. Keep soil consistently moist.

Should I use seed or turf?

Seed is cheaper and offers more variety choices. Turf gives instant results but costs more. Seed is best for large areas; turf for smaller areas or slopes.

Can I sow grass seed on top of existing grass?

Yes, this is called overseeding. Mow short, scarify first, then broadcast seed. Rake in lightly and keep moist. Best done in September in the UK.

GardenCalcs

Lawn Seed Calculator — How Much Grass Seed Do I Need

Calculate how much grass seed you need for a new lawn or overseeding.

Length

Width

Seed Type

Price per kg (optional)

New lawn (vs overseeding)

Include 10% wastage

How We Calculate This

Seed quantity = Area × Application Rate. Rates vary by seed mix type and whether this is a new lawn or overseeding.

New lawn rates: General 35g/m², Fine 25g/m², Hard-wearing 40g/m², Shade 30g/m², Wildflower 5g/m².

Overseeding uses approximately half the new lawn rate. The 10% wastage allowance covers uneven spreading and edge waste.

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates based on standard gardening guidelines. Results may vary with soil conditions, climate, and plant varieties.