Lawn Seed Calculator

Grass seed application rates depend on whether you are creating a new lawn or overseeding an existing one. For new lawns, the typical rate is 35–50 g per m². For overseeding (repairing patches or thickening thin areas), 15–25 g per m² is sufficient. Premium seed mixes with ryegrass tend to use higher rates; fine fescue mixes use lower rates.

This calculator takes your lawn area and purpose to estimate the total weight of seed needed. It also accounts for different seed types: hard-wearing utility mixes (ideal for families and pets), fine ornamental mixes (for low-traffic lawns) and shade-tolerant mixes. Each has a slightly different recommended sowing rate.

The best time to sow grass seed in the UK is April–May or September–October, when soil temperatures are above 8–10°C. Keep the area moist for 2–3 weeks after sowing. Enter your lawn dimensions and choose new lawn or overseed to see the quantity and estimated cost.

How much grass seed do you need? New lawn from bare soil: 50 g/m² (40-50g typical packet rate). Overseeding existing lawn: 20-25 g/m². Sample 100 m² new lawn: 5 kg of seed. Sample 100 m² overseed: 2-3 kg. UK retail packets typically 1-2.5 kg = 25-50 m² coverage. Sowing rate too high wastes seed and crowds seedlings; too low leaves bare patches. Most retail grass seed mixes germinate in 7-14 days at soil temperature 8-15°C — ideal sowing months are April-May and September-October in UK.

UK lawn seed mixes — which to choose? General purpose (perennial ryegrass + fescue + bent): £15-£40/kg, hard-wearing, fast establishment. Hard-wearing/family lawns (high ryegrass content): £20-£50/kg, kid + dog tolerant. Shaded lawns (creeping red fescue, smooth-stalked meadow grass): £25-£60/kg, slower-growing. Fine ornamental (bowling green): high fescue, no ryegrass — £40-£80/kg, demands intensive care. Wildflower meadow mixes: £30-£100/kg — 80% grass + 20% native wildflowers, mowed once or twice yearly.

Soil preparation for new lawns. Existing lawn: kill with glyphosate (where legal) or rotovate. Bare soil: dig over 100-150mm deep, remove stones and roots. Level with rake. Tread firm — light heel-down all over. Final rake to fine tilth. pH ideally 5.5-7.0 (lime if acidic clay). Topsoil top-up: 25-50mm of screened topsoil (£40-£80/m³ delivered) over poor existing soil. Roll lightly with garden roller (or use plank-and-feet method). Time investment: 1 weekend for 100 m² lawn preparation.

Seeding technique step by step. Best months: April or September (warm soil, regular rain). Mix seed with sand 50/50 for visible distribution. Sow half the seed walking N-S, half walking E-W (crosshatch for even coverage). Rake in lightly (1-2cm depth). Water gently — fine spray, never gushing. Keep soil moist for 2-3 weeks until established. First mow when grass reaches 75mm — cut to 50mm (never more than ⅓ of height). Light foot traffic only for 4-6 weeks; full use after 8-12 weeks.

UK lawn care annual calendar. March-April: scarify, aerate, top-dress, feed (high N fertiliser). May-June: weekly mow, weed treat (selective herbicide), overseed thin patches. July-August: water in droughts (or let go brown — recovers in autumn). September: feed (autumn/winter blend, lower N + K), overseed bare patches, scarify lightly. October-November: last cut (raised blade), rake leaves regularly. Winter: stay off frosted/saturated lawn. Annual feed budget: £20-£40 for 100 m² lawn. Weed killers: only as needed, avoid blanket use.