Grass Seed Calculator
Rates vary by species more than by area.
Work out Grass Seed. Rates vary by species more than by area. Free, with no account and nothing to install.
Seed needed
3.5 kg
Perennial ryegrass at 35 g/m² for a new lawn from bare soil
Seeding rates differ by species far more than by area, because seed size varies enormously. Ryegrass seed is large and needs about 35 g per square metre; Kentucky bluegrass seed is tiny and covers the same ground at 15. A single universal rate over-sows one and starves the other. Overseeding an existing lawn takes roughly two thirds of the new-lawn rate, since the established grass is already holding the ground. Scarify first — seed that lands on thatch rather than soil will not germinate, whatever the rate says. Sowing heavier than the recommended rate does not give a thicker lawn. The seedlings compete with each other, and the result is weak, disease-prone grass that thins out within a season.
How the Grass Seed Calculator works
Seed quantity for an area, by species and by whether you are sowing onto bare soil or overseeding. Ryegrass seed is large and needs 35 g per square metre; bluegrass seed is tiny and covers the same ground at 15.
Also known as: how much grass seed do i need · seed for overseeding a lawn · grass seed coverage per bag · how much seed for 100 square metres
Frequently asked questions
How much grass seed do I need per square metre?
It depends entirely on species. Perennial ryegrass needs about 35 g per m² on bare soil, fine fescue 25, and Kentucky bluegrass only 15 — because seed size varies by an order of magnitude between them.
How much seed for overseeding?
About two thirds of the new-lawn rate, since the existing grass is already holding the ground. Scarify first: seed landing on thatch rather than soil will not germinate at any rate.
Can I sow more seed for a thicker lawn?
No — over-sowing gives a worse lawn, not a better one. The seedlings compete with each other for light and water, and the result is weak, disease-prone grass that thins out within a season.
When is the best time to sow grass seed?
Early autumn is best in temperate climates: warm soil, reliable moisture and little weed competition. Spring works but competes with weed germination and risks a dry spell before roots are established.
How long does grass seed take to germinate?
Ryegrass in 5 to 10 days, fescues in 7 to 14, and bluegrass in 14 to 28. Mixtures containing bluegrass look patchy for weeks while the faster species come up first — that is normal rather than a failure.
Put this calculator on your own site
Free to use, on any site, commercial or not. Paste this where you want it to appear. It is a plain iframe, so it works in WordPress, Squarespace, Wix, Webflow, Ghost and anything else that accepts HTML.
<iframe src="https://www.thecalclibrary.com/embed/grass-seed-calculator" width="100%" height="640" style="border:1px solid #e2e8f0;border-radius:12px" loading="lazy" title="Grass Seed Calculator"></iframe>
<p style="font:13px/1.5 system-ui,sans-serif;margin:6px 0 0;color:#64748b">Powered by <a href="https://www.thecalclibrary.com/grass-seed-calculator" style="color:#64748b">Grass Seed Calculator</a> from The Calc Library</p>The only condition is that the credit line below the frame stays in place. That one line is what pays for the tool being free — it is how anyone else finds it.