How the grass seed calculator works
Seed is sown at a rate per unit of ground, printed on the box as grams per square metre in Europe or pounds per 1,000 square feet in North America. The calculator multiplies your lawn area by that rate, halves it if you are only overseeding, and turns the result into kilograms or pounds and a count of packs.
Seed = length × width × sowing rate × (1 for a new lawn, 0.5 for overseeding)Rates differ hugely between species because seed size does: a gram of Kentucky bluegrass holds close to 5,000 seeds, a gram of perennial ryegrass only about 500. So type in the rate from your own mix. The defaults, 35 g/m² and 7 lb per 1,000 ft², suit a typical ryegrass or tall-fescue blend. For reference, 1 lb per 1,000 ft² equals about 4.9 g/m².
Worked example
A back lawn of 15 m × 12 m is 180 m². Sown from scratch at 35 g/m² it needs 180 × 35 = 6,300 g, or 6.3 kg: seven 1 kg boxes, or one 5 kg sack plus two 1 kg boxes. If the lawn is merely thin and patchy, overseeding at half rate needs 3.15 kg. On the US side, a 50 ft × 40 ft lawn is 2,000 ft²; at 7 lb per 1,000 ft² it takes 14 lb of seed, which is five 3 lb bags.
Sowing rates by grass type
| Grass | New lawn rate | Germination | Suited to |
|---|---|---|---|
| Perennial ryegrass | 7–9 lb/1000 ft² (34–44 g/m²) | 5–10 days | Cool climates, heavy wear |
| Tall fescue | 6–8 lb/1000 ft² (29–39 g/m²) | 7–14 days | Cool to transition zones, drought |
| Kentucky bluegrass | 2–3 lb/1000 ft² (10–15 g/m²) | 14–30 days | Cool climates, self-repairing turf |
| Fine fescues | 3–5 lb/1000 ft² (15–24 g/m²) | 7–14 days | Shade, poor soil |
| Bermudagrass (hulled) | 1–2 lb/1000 ft² (5–10 g/m²) | 10–30 days | Hot summers, full sun |
| European lawn mix | 25–40 g/m² | 7–21 days | General garden lawns |
Overseeding rates are roughly half of these figures, because the existing grass already fills much of the ground.
When and how to sow
Cool-season grasses establish best in early autumn, when the soil is still warm (about 10–20 °C, 50–65 °F) and weeds are slowing down; mid-spring is the second choice. Warm-season grasses such as bermuda need soil above about 18–20 °C (65–70 °F), so sow them in late spring. Split the seed into two halves and spread them in perpendicular passes for even cover, rake it in lightly to 3–6 mm (⅛–¼ in), then roll or tread the surface so each seed touches soil.
Mistakes that waste seed
- Sowing extra thick “to be safe”. Crowded seedlings compete for light and water and are more prone to damping-off disease. Stay within 10–20% of the label rate.
- Overseeding onto thatch. Seed sitting on dead grass dries out. Mow short and scarify first so it reaches the soil.
- Using a weed preventer. Many pre-emergent crabgrass products also stop grass seed germinating for weeks; read the waiting interval on the label.
- Letting the surface dry. The top centimetre must stay damp until the grass is up, which can mean two light waterings a day in warm weather.
Frequently asked questions
How much grass seed do I need per square metre?
For a new lawn, 25–40 g/m² for most ryegrass and fescue mixes. For overseeding an existing lawn, about half: 15–20 g/m².
How much grass seed for 1,000 square feet?
Tall fescue needs 6–8 lb, perennial ryegrass 7–9 lb and Kentucky bluegrass 2–3 lb per 1,000 ft² for a new lawn. Use about half those amounts when overseeding.
How far does a 1 kg box of grass seed go?
At 35 g/m², 1 kg sows about 28.6 m² of new lawn, or about 57 m² when overseeding at half rate.
Can you put down too much grass seed?
Yes. Seedlings packed too tightly stay weak and are prone to disease, so doubling the rate rarely gives a thicker lawn; it mostly wastes seed.
How long does grass seed take to grow?
Ryegrass shows in 5–10 days, fescues in 7–14 days and bluegrass in 2–4 weeks. Mow for the first time when the grass reaches about 7–8 cm (3 in), taking off no more than a third.
Last reviewed: 2026-09-27 · How we calculate