Enter the size of the lawn and the sowing rate printed on the seed bag. You get the seed quantity in kilograms and grams, how much that is per 100 m², how many bags of your chosen size that means, and the cost if you add a price. Rates for a new lawn, overseeding and patch repair are one tap away.
From the seed bag. Presets below are typical figures.
To count whole bags.
To get the total and the cost per m².
Enter the lawn area and the sowing rate.
How it works
Grass seed is dosed per square metre, so the arithmetic is area × rate. What varies is the rate: a new lawn from bare soil needs roughly 30–40 g/m², overseeding an existing lawn about half that at 15–25 g/m², and repairing bare patches often 40–50 g/m² because you want fast cover in a small area.
Rates also depend on the mixture. Ryegrass is a large seed, so a ryegrass-heavy mixture needs more grams for the same number of seeds; fine fescues and bentgrass are small-seeded and go further. The bag states the rate the breeder recommends for that mixture, which is why it is an input here rather than a constant.
Bags are counted up to whole units, since that is how seed is sold, and the leftover is shown so you know whether you have enough for a repair later in the season. Cost per m² comes out of the same arithmetic and is the honest way to compare a cheap bag with a good one — a mixture sown at half the rate can be cheaper per square metre despite a higher price per kilogram.
Practical examples
A new 200 m² lawn
At 35 g/m² that is 7 kg of seed, or 3.5 kg per 100 m². Buying 2.5 kg bags means three bags with 0.5 kg left over for repairs.
Overseeding the same lawn
Thickening up an existing 200 m² lawn at 20 g/m² needs only 4 kg — roughly half the seed of a new sowing, because the existing grass is already covering the ground.
A five-ar garden
5 ari is 500 m². A new lawn at 35 g/m² takes 17.5 kg of seed; at 1,200 per kg that is 21,000 in total, or 42 per square metre.
A hectare of amenity grass
Sowing a full hectare at 30 g/m² needs 300 kg — the point where seed is bought by the sack and the rate is worth calibrating carefully.
Frequently asked questions
How much seed does a new lawn need?
Typically 30–40 g/m², which is 3–4 kg per 100 m². Sowing much heavier does not give a better lawn: overcrowded seedlings compete with each other and thin out anyway.
How much for overseeding?
About half a new sowing, commonly 15–25 g/m². The existing turf provides the cover; you are filling gaps and adding fresh varieties, not starting from scratch.
Why does the recommended rate differ between bags?
Because seed size differs by species. Perennial ryegrass has large, heavy seed and needs more grams per m² than a fine fescue mixture to reach the same number of seeds per square metre.
Should I round up when buying?
Yes, and the tool does. A little spare seed stored dry and cool is useful for repairs, and running out mid-job leaves visible stripes when you finish with a different batch.
When is the best time to sow?
Early autumn is usually best — warm soil, cooler air and reliable rain. Spring works too but needs more watering. In midsummer heat, seed germinates unevenly unless you can irrigate daily.
How long until the grass comes up?
Ryegrass can show in 5–10 days, fescues and bluegrass take two to three weeks. Keep the surface consistently moist during that period; a single dry day at germination costs you plants.
Does the tool tell me how much fertiliser to use?
No — for that use the fertilizer calculator, which converts a nutrient target in kg/ha into the product quantity for your area.
How do I measure an irregular lawn?
Split it into rectangles and add the areas, or use the area calculator for triangles and circles. Then enter the total here in m², ari or hectares.
Can I calculate cost per square metre?
Yes, enter the price per kilogram and the result includes the cost per m². It is the fairest way to compare mixtures, because rate and price move in opposite directions.
Is more seed a fix for poor soil?
No. Seed sown onto compacted or unprepared soil fails at any rate. Loosening the top few centimetres, raking level and firming the surface does more for establishment than an extra kilogram.
Does the sowing rate change for shade mixtures?
The bag rate is what matters, and shade mixtures often specify a slightly higher rate. Follow the bag rather than a general rule of thumb.
Is my data uploaded?
No. Everything is calculated in your browser.
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