Grass seed is applied at a rate per square metre, so the amount you need follows directly from your lawn area and whether you are starting a new lawn or overseeding an existing one. This calculator converts that into grams, kilograms and bags.
How it works
area = length × width
grams = area × seed rate (g per m²)
kg = grams / 1000
bags = ceil(kg / bag kg)The seed rate is the lever: a new lawn is sown heavier than an overseed, because a new lawn has bare soil to cover while an overseed only fills gaps in existing turf.
Worked example
A 10 m × 8 m new lawn at 35 g/m², using 1 kg bags:
- Area = 80 m²
- Seed = 80 × 35 = 2800 g = 2.8 kg
- Bags = ceil(2.8 / 1) = 3 bags
What to watch
Timing beats quantity. Sowing into warm, moist soil in spring or early autumn matters more than the exact rate. Cold or dry soil gives patchy germination whatever you sow.
Even spreading. Split the seed into two halves and spread one north-to-south and the other east-to-west for even coverage without visible stripes.