Grass Seed Calculator
Estimate seed quantity for rectangular, circular, elliptical, or triangular lawns.
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CalculatorHow to useFormula & methodWorked exampleStart with the area that will be seededSelect a rate for the actual jobFrequently asked questionsRelated calculatorsSourcesHow to use this calculator
- Choose the lawn shape and the measurement system for its dimensions.
- For a circle enter its radius in the first box; the second dimension is unused. For an ellipse enter its two semi-axes.
- Use the seed manufacturer’s rate for your project, then enter bag mass to estimate the purchase quantity.
Formula and method
For the assumptions behind these results, read the explanation below. You can also explore Sod and Fertilizer.
A worked example
A 10 m by 5 m lawn has an area of 50 m². At 30 g/m² it needs 1,500 g, or 1.5 kg, of seed. A single 5 kg bag covers the calculated requirement.
Start with the area that will be seeded
The seed calculation is a multiplication of area by the application rate. Its quality depends on using dimensions that describe the lawn itself. Paths, patios, ponds, and permanent beds are not areas that need grass seed. Divide a complicated lawn into familiar shapes and add their seed requirements.
A circle’s radius is half its diameter. An ellipse uses semi-axes here: each is half the full width measured through the center. For a triangle, height means perpendicular height from the base to the opposite corner, not the length of a sloping side. These distinctions prevent common area errors before the seed rate is applied.
Select a rate for the actual job
New seeding and overseeding usually use different rates, even for the same product. The mix, germination percentage, seed size, and desired result also affect the manufacturer’s directions. Enter a product-specific rate rather than assuming the default is suitable for all grass types and climates.
The calculated seed requirement remains unrounded, while the purchase count rounds up to whole bags. Extra seed in a purchased bag does not mean it should all be applied. Overly dense seeding can increase competition and is not a substitute for soil preparation, good seed contact, suitable temperature, and consistent moisture during establishment.
Frequently asked questions
What if the lawn is not a perfect shape?
Break it into sections and add the resulting seed masses. A carefully measured approximate area is better than using the surrounding rectangle.
Why are the ellipse inputs semi-axes?
The formula πab requires the center-to-edge distances. If you have full lengths, divide each by two before entering it.
Sources and further reading
- University of Massachusetts Amherst — Seeding Rate Considerations ↗
Reports seeding rates per unit area and explains species, seed quality, establishment conditions, and excessive seeding. The default rate is an arithmetic example, not a universal recommendation.
- National Institute of Standards and Technology — SI conversion factors ↗
Reference for physical unit conversions. The calculator converts measurements before applying its formula.
Our explanations are written for BiologyCalc. Read how we build and check our tools. These calculations are educational estimates where the underlying model requires assumptions.