Lawn Seed Calculator
How much grass seed a lawn needs, by grass type and whether you are sowing new or overseeding.
Seed is sown by weight per area, and the rate depends on the grass: fine-seeded species like Kentucky bluegrass need far less than ryegrass or fescue.
How the lawn seed calculator works
Seed is sown by weight per area, and the rate depends on the grass: fine-seeded species like Kentucky bluegrass need far less than ryegrass or fescue. Overseeding an existing lawn takes about half the rate of a new sowing. The rates here are typical label rates in g/m² (converted to lb per 1,000 ft²); follow the bag if it says otherwise.
Formula: seed = area × rate (× ½ for overseeding)
Worked examples
| Inputs | Seed needed | Note |
|---|---|---|
| 20 × 12 m of ryegrass | 8.4 | 8.4 kg |
| 60 × 40 ft of tall fescue | 14.75 | 14.7 lb |
| Overseeding 300 m² of bluegrass | 1.8 | 1.8 kg |
FAQFrequently asked questions
How much grass seed per square metre?
Typically 25–35 g/m² for a new lawn of ryegrass or fescue and half that for overseeding. Kentucky bluegrass has tiny seeds and needs only 10–15 g/m².
When is the best time to sow?
Spring or early autumn for cool-season grasses, when the soil is warm and moist; late spring for warm-season grasses such as couch and Bermuda.
Why does overseeding need less?
Existing grass fills most of the space, so the seed only has to thicken the sward; sowing at the full rate wastes seed and crowds the seedlings.
My bag is rated in lb per 1,000 ft² — what do I do?
Choose the imperial units. 1 g/m² is about 0.2 lb per 1,000 ft², so a 6 lb per 1,000 ft² bag rate is roughly 30 g/m².
Where these figures come from
- NCBI Bookshelf — Molecular Biology of the Cell — growth kinetics and molecular conventions
- Wellcome Sanger Institute — a leading UK genomics institute
Last checked: September 2026. Formulas are the standard textbook forms; assumptions are stated on each page because they are where these models break.