Lawn Seed Calculator
Calculate exactly how much grass seed you need based on lawn area, grass type, and seeding purpose.
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How to use this calculator
Seeding rates vary by grass species and purpose. New lawns require the full rate; overseeding uses half; patching uses 150% to achieve rapid coverage.
- 1
Measure your lawn area in square metres.
- 2
Select the grass species you are planting.
- 3
Choose whether you are establishing a new lawn, overseeding, or patching.
- 4
The calculator shows seed weight in kg and lbs at the recommended rate.
Frequently asked questions
What formula does the lawn seed calculator use?
Seed in kilograms = lawn area in m² × application rate in g/m² ÷ 1000. The pounds figure is the kilogram result multiplied by 2.20462. No wastage or spreader allowance is added.
Where do the seeding rates come from?
They are fixed per grass type in the tool: fine fescue 30 g/m², tall fescue 40, ryegrass 35, bluegrass 20, zoysia 10, buffalo grass 8 and bermuda 5. Treat them as the figures built into this tool; bag labels, seed mixtures and coated seed vary, so the rate printed on your product takes priority.
How do overseeding and patching change the rate?
Overseeding uses half of the new-lawn rate and patching uses 150% of it. Tall fescue, for instance, moves from 40 g/m² for a new lawn to 20 for overseeding and 60 for patching.
Why do bermuda and fine fescue differ so much?
The tool assigns 5 g/m² to bermuda and 30 g/m² to fine fescue. For a 200 m² lawn that is 1.00 kg against 6.00 kg. The gap reflects the different rates coded into the tool, so check the label of the actual seed you are buying.
Can I enter a mix of grass types?
No. Pick one type per run. For a blend, work out the area share for each component, run them separately and add the weights, or use the blend’s own application rate from its packaging.
Does it recommend when or how to sow?
No. It gives a weight for the area, type and purpose you select. Timing, soil preparation, watering and climate suitability are outside what it calculates.
What area should I enter for patching?
Enter the total area of the bare patches, not the whole lawn. Four square metres of patches in bluegrass comes out at 0.12 kg here, which is 30 g/m² over 4 m².
Working out how much grass seed to buy
Area times rate
Seed quantity is a straight multiplication: the area to be sown multiplied by a rate in grams per square metre. The calculator holds one base rate per grass type, then scales it by purpose. A new lawn takes the full rate, overseeding takes half, and patching takes one and a half times, to give repair spots a denser start. The answer appears in kilograms and pounds. Because the rate depends only on the type and the purpose, the output changes in a predictable way when you switch one setting, which makes it easy to compare what a different grass choice or a lighter overseeding pass would cost in seed.
Rates the tool applies
The table shows every application rate in grams per square metre for each of the seven grass types and the three purposes, as returned by the calculator. They are fixed values in the code.
| Grass type | New lawn | Overseeding | Patching |
|---|---|---|---|
| Tall fescue | 40 | 20 | 60 |
| Ryegrass (perennial) | 35 | 17.5 | 52.5 |
| Fine fescue | 30 | 15 | 45 |
| Kentucky bluegrass | 20 | 10 | 30 |
| Zoysia | 10 | 5 | 15 |
| Buffalo grass | 8 | 4 | 12 |
| Bermuda | 5 | 2.5 | 7.5 |
Worked results
The next table lists five jobs run through the calculator, each with a different grass type, area and purpose.
| Job | Rate | Seed (kg) | Seed (lb) |
|---|---|---|---|
| 50 m² tall fescue, new lawn | 40 g/m² | 2.00 | 4.41 |
| 120 m² ryegrass, overseeding | 17.5 g/m² | 2.10 | 4.63 |
| 4 m² bluegrass, patching | 30 g/m² | 0.12 | 0.26 |
| 200 m² bermuda, new lawn | 5 g/m² | 1.00 | 2.20 |
| 200 m² fine fescue, new lawn | 30 g/m² | 6.00 | 13.23 |
What the examples show
The last two rows have identical areas and purposes but differ by a factor of six in seed weight, driven purely by the type selected. The ryegrass overseeding job sows 120 m² with a little more seed than the 50 m² new tall-fescue lawn, even though it uses under half the per-metre rate, because the area is more than double. Always sanity-check that a kilogram total matches the pack sizes on sale.
Limits to keep in mind
The tool does not adjust for germination rates, seed coatings, mixtures or the slope and shade of your site. Seed cost, bag size and sowing dates are also outside its scope. Where the packaging gives an application rate for your product, use that rate to cross-check the output, and round the purchase up to whole bags. Measure the lawn as the sown area only, leaving out paths, beds and any section that is already dense, since extra seed on healthy turf is simply wasted.
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Results are estimates for informational purposes only and do not constitute professional financial, medical, legal, or technical advice. Read full disclaimer →