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About this tool
Work out grass seed in kilos for any lawn area from species sowing rate, purity, germination and wastage.
Grass seed is sold by weight but sown by rate, and this calculator converts one into the other: it takes the published sowing rate for your species, adjusts it for whether you are starting a lawn or overseeding, corrects for the pure live seed figure on the bag (purity multiplied by germination), adds a wastage allowance and returns kilograms and bag count. Rates are the standard pounds-per-1000-square-feet ranges converted at 1 lb/1000 sq ft = 4.88 g/m².
Open Lawn Seed Quantity Calculator on AltFTool — it loads instantly in your browser.
Enter the values you already know.
Fine-tune the options to match your scenario.
Read the result and use it in your planning or reporting.
Kentucky bluegrass at 15 g/m² and tall fescue at 35 g/m² are not interchangeable — the tool uses the published figure for each.
Applies the purity and germination printed on the label, so poor seed is compensated for instead of quietly under-sowing.
Rounds up to whole bags at your bag size and shows the spend, which is what you actually take to the nursery.
Between 2 and 35 g/m² depending on species: about 35 g/m² for perennial ryegrass and tall fescue, 22 g/m² for fine fescue, 15 g/m² for Kentucky bluegrass, and only 5–10 g/m² for Bermuda and zoysia because their seed is far smaller. Overseeding an existing lawn uses roughly half these rates.
Pure live seed is purity multiplied by germination — a bag that is 98% pure with 85% germination is 83% pure live seed, so 17% of the weight will never produce a plant. Comparing two bags on price per kilogram of pure live seed rather than per kilogram is the honest comparison.
Sow at the recommended rate, not above it. Over-seeding crowds the seedlings so they compete for water and light, produces thin spindly grass and raises the risk of damping-off disease; under-seeding leaves gaps for weeds. Extra seed is only justified as a wastage allowance, typically 5–15%.
Warm-season grasses such as Bermuda, zoysia and centipede need soil above about 20°C, so February to April or just after the first monsoon rains work best. Cool-season ryegrass and fescue are usually sown October to November in northern India, and are often used to overseed a dormant Bermuda lawn for a green winter.
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