Work out exactly how much grass seed you need for a new lawn, repairs or overseeding. Enter your area and we calculate the kilograms required, then price the best-value boxes and trade bags.
New lawns need around 35 grams per square metre; overseeding an existing lawn takes roughly half that. Sowing too thinly gives a patchy lawn that weeds colonise — measure once, sow once.
01 — The Calculator
Pick a material, pace out your plot, and the value engine prices every way to fill it — hippo bags, dumpy bags or handy sacks.
Seed is far cheaper per m² — sow at 35g/m² in spring or autumn and keep it watered.
When to sow grass seed
Best months: March–May and late August–October — soil needs to be 8°C or warmer to germinate.
Avoid frost and summer heatwaves. Keep the surface moist for 2–3 weeks until established.
Enter dimensions to calculate.
Lawn area
0.0 m²
Seed needed
0.0 kg
Wastage
+10%
Boxes & bags
0 packs
Enter your plot dimensions and the value engine will price the cheapest way to cover it.
Worked example: 40m² family lawn
A 40m² lawn sown from scratch at 35g/m² needs 1.4kg of seed. The calculator matches that against 1kg boxes (each covering about 28m²) and larger trade bags, and shows the cheapest way to cover the area — typically a tenth of the cost of turfing it.
Around 35g per m² for a new lawn (a 1kg box covers roughly 28m²), and 15–25g per m² for overseeding an existing lawn. Always check the pack — hard-wearing rye mixes and fine fescue blends differ.
Garden Calculator — Project
My garden project · 27 September 2026
| Item | Qty | Each | Total |
|---|---|---|---|
| Estimated total | £0.00 | ||
Prices from the Garden Calculator sample trade catalogue — confirm with your merchant before ordering.