Grass Seed Calculator

Work out how much grass seed to buy for a new lawn or to overseed a tired one.

How it works

The grass seed needed is simply the area in square metres multiplied by the sowing rate in grams per square metre:

Grams = length m × width m × rate (g/m²)

A typical rate for a new lawn from seed is around 35 g per square metre; for overseeding an existing lawn, 25 g per square metre is usually enough. Check the rate on your seed packet, as it varies by mixture. Sow in spring or early autumn when the soil is warm and moist.

This tool is a planning aid and simply does the maths from the numbers you enter. Order a little extra to allow for settling. Page updated 18 Sep 2026.