Free farm tool
Seed Rate Calculator
Set your target plant population, the seed lot's TGW, and expected establishment - get the drilling rate in kg/ha and kg/acre.
Seeds to drill
294 /m²
Seed rate
141 kg/ha
Per acre
57 kg/acre
250 plants/m² ÷ 85% establishment = 294 seeds/m², × 48 g TGW ÷ 100 = 141 kg/ha.
The formula
Seed rate (kg/ha) = seeds/m² × TGW (g) ÷ 100, where seeds/m² = target plants/m² ÷ establishment (as a fraction). The logic runs backwards from what you want standing in spring: decide the plant population, allow for the seeds that won't make it, then convert seed count into weight using this lot's actual TGW.
Drilling by weight without checking TGW is the classic shortcut. It works until the year the seed comes up smaller or bigger than usual - then the flat 160 kg/ha you always drill delivers a population a long way from what you intended.
Worked example
| Step | Figure |
|---|---|
| Target population (mid-October wheat) | 250 plants/m² |
| Expected establishment | 85% |
| Seeds needed: 250 ÷ 0.85 | 294 seeds/m² |
| TGW (from the seed label) | 48 g |
| Seed rate: 294 × 48 ÷ 100 | 141 kg/ha (~57 kg/acre) |
Closing the loop
The establishment percentage is the soft number in the formula, and the only way to firm it up is your own history: spring plant counts against drilled seed rates, field by field, year by year. The same habit of per-field records that explains why one field yields more than another also tells you which fields need the extra 10% of seed. If you work in acres, the area converter keeps the units straight.
Frequently asked questions
How do you calculate seed rate in kg/ha?
Divide your target plant population by expected establishment to get seeds per square metre, then multiply by the thousand grain weight in grams and divide by 100. For example: 250 plants/m² at 85% establishment needs 294 seeds/m²; at a TGW of 48g that's 141 kg/ha.
What is a typical wheat seed rate?
Winter wheat is commonly drilled at anywhere from 250 to 400+ seeds/m² depending on drilling date, seedbed condition, and expected losses - later drilling and rougher seedbeds need more. In kg/ha that's roughly 120–200 kg/ha at typical TGWs, but the seeds/m² figure is the one to fix first.
Why does thousand grain weight matter?
Because seed lots vary. A 45g TGW and a 55g TGW differ by over 20% in weight for the same seed count - drill both at a flat 160 kg/ha and one field gets a fifth more plants than the other. TGW is printed on certified seed labels; for home-saved seed, weigh a counted sample.
What establishment percentage should I use?
Typically 60–90%. Use the higher end for early drilling into good seedbeds, and drop it for late drilling, heavy or cloddy land, known slug pressure, or grazing pigeons. Your own records are the best guide - count plants in spring against what you drilled.
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