What happens if I sow too much seed?

Overseeding too heavily makes seedlings compete for light, water, and nutrients, producing weak, thin grass more prone to disease. More seed doesn't mean a thicker lawn.

How much extra should I buy?

A 5–10% buffer covers edges, uneven spreading, and a small touch-up. Grass seed stores well in a cool, dry place for the next season.

When is the best time to sow?

Early autumn and mid-spring are ideal, when soil is warm and moist but not baking. Avoid the peak of summer heat and hard frost.

Do I need to cover the seed?

A light rake to mix seed into the top of the soil improves contact and germination. A thin layer of soil or compost also helps retain moisture and deters birds.

How Much Grass Seed Do I Need? Seed Rate by Lawn Area

Published 1/9/2026 · 3 min read · Everyday calculators

Marco Bianchi — Home, DIY & motoring writer at Allin

Renovation · Materials

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In short

Multiply your lawn area by the recommended seed rate on the packet. A new lawn typically needs about 1 oz of seed per square yard (roughly 35 g/m²), while overseeding an existing lawn uses about half that. For a 1,000 sq ft new lawn that's roughly 7 lb of seed; the exact rate depends on the grass species.

A grass seed head in close-up against a dark field. — Wyxina Tresse · Pexels · Pexels

Work out how much grass seed to buy from your lawn area and the seed rate — with different rates for a new lawn versus overseeding.

Measure your lawn area first

Everything starts with area. For a rectangular lawn, multiply length by width. For an L-shape or a garden with beds cut into it, break the space into rectangles, work out each one, and add them together — then subtract paths, ponds, and flower beds you won't be seeding.

New lawn vs overseeding

The two jobs use very different amounts. Seeding bare ground for a new lawn needs full coverage — roughly 1 oz per square yard as a common starting point. Overseeding a thin but living lawn only fills gaps, so you use about half the rate. Applying full new-lawn rate on top of existing grass wastes seed and can leave patches too crowded.

Why the species changes the rate

Grass seeds vary enormously in size and vigour, so a single universal rate doesn't exist. Fine fescues have tiny, numerous seeds and need less by weight; ryegrasses have larger seeds and need more. Always trust the rate printed on the specific bag you buy, and treat the general figures here as a sanity check rather than a rule.

Worked with our own calculator

Grass seed calculator

Given

Grass type: Kentucky bluegrass
Lawn area: 512 m²

Result

New lawn — seed needed: 5 kg
Overseeding — seed needed: 2.5 kg

These figures are produced by the calculator below, not typed in by hand — they are recomputed whenever the tool changes.

Run it on your own figures →

Frequently asked questions

What happens if I sow too much seed?: Overseeding too heavily makes seedlings compete for light, water, and nutrients, producing weak, thin grass more prone to disease. More seed doesn't mean a thicker lawn.
How much extra should I buy?: A 5–10% buffer covers edges, uneven spreading, and a small touch-up. Grass seed stores well in a cool, dry place for the next season.
When is the best time to sow?: Early autumn and mid-spring are ideal, when soil is warm and moist but not baking. Avoid the peak of summer heat and hard frost.
Do I need to cover the seed?: A light rake to mix seed into the top of the soil improves contact and germination. A thin layer of soil or compost also helps retain moisture and deters birds.

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