Seed calculator
Grass Seed Calculator UK
Work out exactly how much grass seed you need
For new lawns, overseeding, or patch repairs. Draw your lawn on the map or enter your area manually.
Built with 30+ years of professional turf experience
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Seed Calculator
Based on your lawn measurements
Your Lawn Area
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square metres
New Lawn (bare soil)
Starting from scratch
35 g/m²
Overseeding
Thickening up existing grass
20-35 g/m²
Patch Repair
Filling bare spots
40 g/m²
Mostly Bare
35 g/m²
Thin & Patchy
25 g/m²
Needs Thickening
15 g/m²
UK Grass Seed Rates by Type
A quick reference for common UK grass seed types. These are typical rates. Always check the specific product you're using.
| Grass Type / Mix | New Lawn (g/m²) | Overseeding (g/m²) | Best For |
|---|---|---|---|
| Dwarf Perennial Ryegrass Most Common | 30-35 | 20-25 | Family lawns, high traffic |
| Hard-Wearing Ryegrass Mix | 35-40 | 20-25 | Kids, dogs, heavy use |
| Fine Fescue Mix (Ornamental) | 30-35 | 15-20 | Low traffic, display lawns |
| Fescue & Bent (Traditional Fine) | 30-35 | 15-20 | Luxury lawns, cylinder mowing |
| Shade & Difficult Areas Mix | 30-35 | 20-25 | Under trees, north-facing gardens |
| Pure Bent Grass (Agrostis) | 8-10 | 4-5 | Golf greens, bowling greens |
| Wildflower & Grass Mix | 3-5 | 2-3 | Meadow areas, wildlife |
Rates based on UK trade guidelines. We recommend 30 g/m² as a good all-round starting point for most dwarf ryegrass mixes (range 25-35 g/m²).
Grass Seed Calculator: Common Questions
For most UK lawns using a dwarf ryegrass mix, 30 g/m² is a solid starting point. The range is 25-35 g/m² depending on your seed type and how thick you want coverage. For overseeding into existing grass, 15-25 g/m² is usually plenty. Pure bent grass is much lower at 8-10 g/m² because the seed is tiny.
The two best windows are spring (April to May) and early autumn (September to early October). Autumn is often better because the soil is still warm from summer, the air is cooler so there's less stress on seedlings, and you get reliable rainfall. The key is soil temperature: grass seed needs at least 8°C to germinate. Avoid sowing in midsummer heat or winter cold.
A new lawn on bare soil needs more seed because you're building the entire grass cover from nothing. 30-35 g/m² is typical. Overseeding goes into existing grass, so you need less because the existing lawn is already doing some of the work. 15-25 g/m² depending on how thin the lawn is. After a heavy scarify where you've removed a lot of material, go closer to the new lawn rate.
More is not always better. Sowing too heavily creates overcrowded seedlings that compete with each other for light, water, and nutrients. They end up thin and weak instead of thick and strong. Stick to the recommended rate. The plants will tiller and spread to fill in. That said, going slightly over (10-15%) is fine as insurance against bird losses and uneven spreading.
Split your total seed into two equal halves. Sow the first half walking north to south across your lawn, then sow the second half walking east to west. This cross-hatch pattern gives you much more even coverage than one pass. For larger areas, a hand-held broadcast spreader makes the job easier and more consistent.
A pre-seeder fertiliser is high in phosphorus, which drives root development in new seedlings. Apply it before or at the time of sowing. It gives your new grass the best possible start. Once the grass is established and you've had your first few mows, switch to a seasonal feed like Spring Starter Plus or Autumn Lawn Builder depending on the time of year.
Ryegrass is the quickest at 7-14 days in good conditions. Fescue takes a bit longer, usually 14-21 days. Bent grass can be 14-28 days. These times depend on soil temperature, moisture, and seed-to-soil contact. Keep the seedbed moist (not waterlogged) until you see consistent germination. Don't panic if it takes longer in cooler weather.
Where to Buy Grass Seed
We use BS Premier Lawn Grass Seed in our videos. That's from our friends at Boston Seeds, who sponsor the Premier Lawns YouTube channel. We don't sell grass seed at iGrow Carpet (we focus on fertilisers), but Boston Seeds are our go-to recommendation for quality UK seed. Once you've got your seed sorted, come back and we'll make sure you've got everything else your lawn needs.
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