What This Calculator Does
The Grass Seed for a Rectangular Lawn Calculator tells you exactly how much grass seed to buy for a rectangular patch of ground. Enter the lawn's length and width plus the recommended seeding rate, and it returns the total seed required in both grams and kilograms — taking the guesswork out of sowing a new lawn or overseeding an existing one. The tool uses metric units (metres and grams per square metre) so it works anywhere; just match the seeding rate to your seed brand's label.
How to Use It
Measure the length and width of your lawn in metres. Check your grass seed bag for the recommended sowing rate — typical figures are around 25–35 g/m² for a new lawn and 15–25 g/m² for overseeding. Enter all three values and read off the result. Buy a little extra to allow for edges, patches, and birds.
The Formula Explained
First the area is found by multiplying length by width. The seed quantity is then the area multiplied by the seeding rate: $$\text{Seed} = (\text{Length} \times \text{Width}) \times \text{Rate}$$ Because the rate is given in grams per square metre, the raw answer is in grams; dividing by 1,000 converts it to kilograms.
Worked Example
For a lawn 10 m long and 5 m wide sown at 35 g/m²: area = \(10 \times 5 = 50\) m². $$\text{Seed} = 50 \times 35 = 1{,}750 \text{ g} = 1.75 \text{ kg}$$ So you would buy about 2 kg of grass seed to cover the lawn with a small buffer.
FAQ
What seeding rate should I use? Follow your seed packet. As a rule of thumb, use a higher rate (30–35 g/m²) for a brand-new lawn and a lower rate (15–25 g/m²) when overseeding thin grass.
Can I use feet instead of metres? This tool expects metres. Convert feet to metres by multiplying by 0.3048 before entering, and use a rate expressed in grams per square metre.
Should I buy extra seed? Yes — add 5–10% to cover edges, uneven coverage, and seed lost to birds or wind.
