Grass seed calculator
Work out how much grass seed you need to sow or overseed a lawn, from its area and your chosen seeding rate.
Result
Grass seed required
How to use this calculator
- Measure the length and width of the lawn area.
- Choose a seeding rate — lower for overseeding an existing lawn, higher for sowing a new one from bare soil.
- Read the total seed weight required.
Assumptions
- The default 35g/m² is a general-purpose rate — always check the specific seed product's own recommended rate, since mixes vary.
Technical details: what the fields mean
- Length
length - The longest side of the lawn area.
- Width
width - The other side of the lawn area.
- Seeding rate
seedingRate - Seed weight per square metre — roughly 25g/m² for overseeding a thin lawn, 35g/m² for general use, 50g/m² for a new lawn from bare soil.
Methodology
Seed required = area × seeding rate. Rates vary by grass seed mix — check the specific product's recommended rate for the most accurate figure.
Worked example
10m × 6m lawn, 35g/m² rate
Inputs: length=10, width=6, seedingRate=35
Result: 2.10 kg of seed required
Practical guidance
- Sow in spring or early autumn when soil is warm and moist for the most reliable germination.
- Rake and lightly water the area before and after sowing for even coverage.
Common mistakes
- Sowing too thickly, which wastes seed and can cause overcrowded, weak seedlings.
- Sowing in mid-summer heat or winter cold, when germination is unreliable.
FAQs
How much grass seed do I need per square metre?
Roughly 25–50g/m² depending on whether you're overseeding an existing lawn or sowing a new one — this calculator multiplies by your exact area.
What's the best time to sow grass seed?
Spring or early autumn, when soil is reliably warm and moist.