Lawn Overseeding Calculator
Calculate seed quantity, preparation steps, and timing for lawn overseeding.
How We Calculate This
Seed rate depends on lawn condition: lightly thin areas need about 15 g/m², patchy lawns 25 g/m², and heavily worn or scarified lawns 35 g/m². These sit inside the standard UK overseeding band of roughly 15-25 g/m² for a top-up and 35-50 g/m² for heavy renovation (RHS lawn repair; Lawnsmith seeding rates).
The base rate is fine-tuned for grass type — fine fescue and bent mixes have smaller, lighter seed so cover the same area with fewer grams (×0.8), while ryegrass-heavy hardwearing mixes use a little more (×1.1). A waste factor (default 10%) is added for uneven spreading, then the total is divided by your chosen bag size to give whole bags. Estimated cost is based on the actual seed weight required, not the rounded-up bag weight.
Germination timing follows season and soil temperature: perennial ryegrass germinates in about 7-10 days once soil is above ~8-10°C, with fescues a little slower. Autumn (warm soil, reliable moisture) is the most dependable window in the UK.
Frequently Asked Questions
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Last updated: March 2026
All calculations are estimates based on standard gardening guidelines. Results may vary with soil conditions, climate, and plant varieties.