Free Seed Rate calculator with clear step-by-step results.
Seed rate is driven by target plant population divided by establishment percentage, which is laboratory germination multiplied by the fraction that survives field conditions. Multiplying by thousand seed weight converts seeds per square metre into kilograms per hectare.
Seeds to sow
Seeds/m2 = target plants / (germination x (1 - field loss))
Seed rate
kg/ha = seeds per m2 x thousand seed weight x 10 / 1000
It differs by species and by season - wheat can range from 38 to 55 grams. Drilling by weight without checking it can leave the population 30% out.
Around 10-15% in good conditions with a fine seedbed, and 25% or more for late drilling into cold wet soil or a cloddy surface.