Sowing by weight is the norm for cereals, cover crops and lawns, but seed size varies a lot between varieties and lots. Using thousand-seed weight gets the plant population right.
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Enter your target plants, thousand-seed weight, germination and establishment. The calculator gives the seeding rate and the total seed for your area.
seeds per m² = target plants ÷ (germination × establishment) g per m² = seeds per m² × thousand-seed weight ÷ 1,000 kg/ha = g per m² × 10
Thousand-seed weight is the weight in grams of 1,000 seeds; it varies with variety and growing season.
Wheat at 250 plants/m² with a 45 g thousand-seed weight, 95% germination and 85% establishment needs 310 seeds/m²: 139 kg/ha, or 279 kg for 2 ha.
Divide target plants by germination and establishment to get seeds, then multiply by seed weight.
The weight of 1,000 seeds in grams. Larger seeds need a higher kg/ha for the same plant numbers.
Often 100–180 kg/ha (about 90–160 lb/acre), depending on seed size and timing.
Not every germinating seed becomes a healthy plant in the field.
Divide the plants you want by germination (and establishment), then multiply by seed weight.
Target plants per acre ÷ expected emergence: for 32,000 plants at 95%, plant about 33,700 seeds per acre.