Grass Seed Calculator
Seed for a lawn from rectangles, circles or areas typed one per line and the rate on your bag (lb per 1 000 sq ft or kg per 100 m²), with waste, bags and cost.
Total area, pounds or kilograms of seed with the waste allowance, bags rounded up and their coverage, cost, fertiliser at your rate and the cubic yards or m³ of top-dressing for the depth you set.
Example: A 40 × 25 ft lawn, a 20 ft circle and 300 sq ft more are 1 614 sq ft: at 4 lb per 1 000 that is 6.5 lb, 6.8 lb with 5 % waste — one 10 lb bag (covers 2 500 sq ft); a ¼ in top-dress takes 1.25 yd³.
The rate on the bag,
times your area.
How the areas are measured, why the rate must be yours, and what the extras cover.
Area and rate
Lines are rectangles (width × height), circles (diameter) or plain areas, summed. Seed = area ÷ 1 000 sq ft (or 100 m²) × the rate printed on your bag; the page holds no rate because it varies enormously — a fescue mix for a new lawn, ryegrass, a bentgrass green and an overseeding rate on the same mix can differ by a factor of ten. The waste allowance covers spreader overlap, edges and bird loss.
Bags and cost
Bags are rounded up to whole bags of the size you buy; the coverage of one bag (bag ÷ rate × the area unit) shows when a smaller bag would do. Cost is bags × the price you enter. A starter-fertiliser rate from its label and a top-dressing depth (area × depth as cubic yards or m³) are optional extras with the same arithmetic.
What it is not
No agronomy: species choice, timing, soil preparation and germination depend on your climate and are not judged here. A light ¼ in / 5 mm top-dress keeps seed-to-soil contact; deeper burial stops germination. Nothing leaves the browser; the same four anonymous usage counts as the rest of the site apply.
SOURCES
- Seed = area ÷ 1 000 sq ft (or 100 m²) × the rate printed on your bag × (1 + waste); bags rounded up; top-dress volume = area × depth; no species rate assumed
Last reviewed 22 September 2026. How results are checked: How we verify.