How this calculator works
Seed mass is lawn area multiplied by the application rate. Rates differ with seed size, species, purity, germination, coating and whether the job is a new lawn or overseeding. UMass Extension explains why the bag weight alone is not a measure of pure live seed. Use the label or a local extension rate that matches the seed product; this page deliberately leaves the rate editable.
Formula
Seed mass (kg) = area (m2) × rate (g/m2)/1000. Area = seed mass/rate after conversion to kg/m2. For lb/1000 ft2, multiply by 0.45359237/92.90304 to get kg/m2.
Worked example
A 100 m2 lawn at 20 g/m2 needs 2 kg of seed. A 3 kg bag applied at 30 g/m2 covers 100 m2.
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Frequently asked questions
Should I double the rate for overseeding?
Do not assume that. Overseeding commonly needs a different rate from establishment; use guidance for your turf and conditions.
Do coated seeds change the required bag mass?
They can. Coating increases product weight without adding more seeds. Match the rate to the product label.
Can I use an irregular lawn shape?
Choose a measured area or split the lawn into simple shapes. The tool also supports circles, ellipses, triangles, trapezoids and rings.