Lawn
Grass Seed Calculator
Find how many pounds of grass seed you need for new seeding or overseeding, by area and seed type.
Your answer
Sow half the seed walking north to south and half east to west. It is the simplest way to avoid the striped, patchy result of a single pass.
How much seed a lawn actually needs
Seed is applied by weight per unit area, and the correct rate depends on two things: how big the individual seeds are, and whether there is existing grass already occupying the space. Bermuda seed is tiny, so a kilogram covers a huge area. Fine fescue is heavier per seed and sown thicker.
| Seed type | New lawn | Overseeding | Character |
|---|---|---|---|
| Perennial ryegrass | 35 g/m² | 25 g/m² | Germinates in 5-10 days, tough underfoot |
| Fescue / rye mix | 35 g/m² | 25 g/m² | The reliable all-rounder |
| Fine fescue | 40 g/m² | 28 g/m² | Shade tolerant, fine leaf, low traffic |
| Bermuda | 10 g/m² | 7 g/m² | Warm season only, spreads by runners |
More seed is not better
Oversowing creates seedlings competing with each other for light, water, and nutrients before they have any root system. The result is a dense flush that thins dramatically under the first stress, and it is far more prone to damping-off disease than a correctly sown area.
Preparation matters more than the seed you buy
- Mow short and scarify to expose soil — seed on thatch does not germinate.
- Aerate if the ground is compacted, hollow-tine for anything heavily used.
- Rake to a fine tilth on bare ground; seed needs contact with soil, not with dust.
- Sow in two passes at right angles for even coverage.
- Rake lightly or top-dress 3-5 mm — seed buried deeper will not emerge.
- Keep the surface consistently moist for three weeks, never soaked.
Timing is the biggest single variable
Cool-season grasses germinate best in soil around 10-18°C. Late summer delivers that with the ground still warm from summer and the air cooling — the opposite of spring, where soil lags behind air and seedlings hit summer heat within weeks. Warm-season grasses reverse this and want late spring.
Common mistakes
- Sowing onto thatch or unscarified turf, so most seed never reaches soil.
- Letting the surface dry out once during the germination window.
- Sowing in a heatwave or on frozen ground.
- Using a shade mix in full sun, or a ryegrass mix under dense trees.
- Walking on the new lawn before the first cut, which is at about 7 cm of growth.
How much grass seed do I need per square metre?
Roughly 35 g/m² for a new lawn and 25 g/m² for overseeding with a ryegrass mix. Fine fescue mixes go down heavier, and bentgrass far lighter.
When is the best time to sow grass seed?
Late summer to early autumn for cool-season grasses: soil is still warm, air is cooling, and weed competition is at its lowest. Spring is second best.
Can I put down seed and weed-and-feed together?
No. Pre-emergent weed control prevents grass seed germinating as effectively as it prevents weeds. Leave at least six weeks between the two.
How long until new grass is established?
Germination in 5-21 days depending on species and temperature, a usable lawn in about eight weeks, and full establishment across a season.
Last reviewed February 2026