Grass Seed Calculator

Work out how much grass seed you need for a new lawn or overseeding based on lawn area and sowing rate.

Part of:Landscaping hubGardening hub
ft
ft
g/m²

How to Use This Calculator

How to Use

  1. Choose metric or imperial units.
  2. Enter the length and width of your lawn area.
  3. Pick whether you are sowing a new lawn or overseeding an existing one — this sets a typical sowing rate.
  4. Adjust the sowing rate if your seed bag recommends a different figure.

Typical sowing rates

  • New lawn from bare soil: 30–50 g/m² (we use 35 g/m²)
  • Overseeding an existing lawn: 15–25 g/m² (we use 20 g/m²)

Always check the rate printed on your seed bag, as it varies by grass mixture.

Common Questions

How much grass seed do I need per square metre?

For a brand new lawn allow roughly 35 grams per square metre. For overseeding a thin lawn, around 20 grams per square metre is usually enough.

When is the best time to sow grass seed?

Early autumn and mid spring are ideal, when the soil is warm and moist but not baked or frozen.

Should I buy extra seed?

It is worth buying a little extra to patch any thin areas a few weeks after sowing.

How much grass seed do I need per square metre?

Around 35 g per m² for a new lawn and about 25 g per m² for overseeding an existing lawn. The calculator works out the total for your area.

When is the best time to sow grass seed?

Spring and early autumn are ideal, when the soil is warm and moist. Avoid sowing in frost or the height of summer.

Related Calculators