The standard grass seed rate for UK lawns is 20–50 grams per square metre (g/m²), depending on the seed mix and whether you’re establishing a new lawn or overseeding. Fine ornamental lawns need less seed (20–35 g/m²) while hard-wearing ryegrass family lawns need more (35–50 g/m²).
Enter your lawn dimensions in metres and get results in kilograms.
Open CalculatorQuick Reference Table (Metric)
This table shows how much grass seed (in kilograms and grams) you need for common UK garden sizes. Rates are for new lawn establishment.
| Lawn Size (m²) | Ryegrass Mix (50 g/m²) | Ryegrass/Fescue Blend (35 g/m²) | Fine Fescue (25 g/m²) | Overseed Rate (~17 g/m²) |
|---|---|---|---|---|
| 10 m² | 500 g | 350 g | 250 g | 170 g |
| 25 m² | 1.25 kg | 875 g | 625 g | 425 g |
| 50 m² | 2.5 kg | 1.75 kg | 1.25 kg | 850 g |
| 100 m² | 5 kg | 3.5 kg | 2.5 kg | 1.7 kg |
| 200 m² | 10 kg | 7 kg | 5 kg | 3.4 kg |
| 500 m² | 25 kg | 17.5 kg | 12.5 kg | 8.5 kg |
How to Measure Your Lawn in Square Metres
For a rectangular lawn, measure the length and width in metres and multiply them together. A lawn that is 12 m long and 8 m wide = 96 m².
For irregular shapes:
- Break the lawn into rectangles and triangles
- Calculate each section’s area separately
- Add them together for the total
- Use a measuring wheel for curved edges
The average UK back garden is approximately 188 m² (about 14 m × 13.5 m). A small terraced house garden may be 20–50 m², while a detached property garden could reach 300–500 m². Semi-detached gardens average around 100–150 m².
Seeding Rate by Grass Mix (UK-Common Species)
UK lawn seed is typically sold as pre-mixed blends rather than single species. Here are the most common categories:
| Mix Type | Key Species | New Lawn (g/m²) | Overseed (g/m²) | Best For |
|---|---|---|---|---|
| Hard-Wearing / Family | Perennial Ryegrass + Tall Fescue | 35–50 | 17–25 | Play areas, pets, high traffic |
| General Purpose | Ryegrass + Fescue blend | 30–40 | 15–20 | Most UK gardens |
| Ornamental / Fine | Creeping Red Fescue + Browntop Bent | 20–35 | 10–17 | Show lawns, low traffic |
| Shaded Areas | Fine Fescue + Rough-Stalked Meadow Grass | 25–35 | 12–17 | Under trees, north-facing |
| Wildflower Meadow | Fine grasses + wildflower mix | 3–5 | N/A | Low-maintenance, biodiversity |
New Lawn vs. Overseeding Rates (g/m²)
Overseeding uses approximately half the new-lawn rate. This is because existing turf already covers much of the ground — adding the full rate would overcrowd the seedlings.
For full overseeding guidance including timing, step-by-step instructions, and common mistakes, see our overseeding calculator guide.
Frequently Asked Questions
How many m² does a 20 kg bag cover?
At a new-lawn rate of 35 g/m², a 20 kg bag covers about 571 m². At an overseeding rate of 17 g/m², the same bag covers approximately 1,176 m². For fine fescue mixes at 25 g/m², a 20 kg bag covers around 800 m².
What seed rate for a shaded UK garden?
Use a shade-tolerant mix (Fine Fescue + Rough-Stalked Meadow Grass) at 25–35 g/m². These species tolerate low light conditions much better than ryegrass. Avoid sowing under dense conifer canopies where very little light penetrates.
When is the best time to sow grass seed in the UK?
September is the ideal month for sowing grass seed in the UK. The soil is still warm from summer, autumn rain provides natural moisture, and weed competition is lower. Spring (April–May) is the second-best window.