Seed rate calculator
million/ha
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Seed rate
Sowing value
A worked example is filled in. Take the target seed count from your regional recommendations.
In short
To calculate seed rate in kg/ha, take the number of millions of viable seeds you want per hectare, multiply it by the thousand seed weight in grams, multiply by 100 and divide by the sowing value of the seed lot.
Sowing value is germination times purity divided by 100, so a lot that is not fully clean and alive needs more weight to reach the same stand. A local guide gives the seed count and the lot analysis gives the rest. In Planva, thousand seed weight, germination and purity sit in the seed catalogue, and the agroplan holds seed by rate or quantity, planned and actual.
The formula
Seed rate in kg/ha = million viable seeds per hectare × thousand seed weight (g) × 100 ÷ sowing value. Sowing value = germination × purity ÷ 100, with germination and purity read from the lot analysis on the 100-point scale. A lot with germination 94 and purity 98 has a sowing value of 92.1.
The extra steps matter. One million seeds that weigh 40 g per thousand come to 40 kg. Seed counts in guides assume every seed is clean and alive. Dividing by sowing value adds the weight needed to cover seed that is neither.
The calculator takes millions of viable seeds per hectare, thousand seed weight, germination and purity. It has no separate survival field. To reproduce the worked example below, enter 2.5 million, 35 g, 85 for germination (standing in for survival) and 100 for purity. You get 103 kg/ha.
The same sum from plants per square metre
Many extension services state the goal as plants per square metre and subtract field losses. Alberta Agriculture gives the metric form as seeding rate in kg/ha = plants per m² × thousand kernel weight (g) ÷ seedling survival (as a decimal) ÷ 100. One million seeds per hectare is 100 per square metre, so both routes agree as long as survival and sowing value describe the same losses. Saskatchewan Pulse Growers use the same logic for peas: 85 plants/m² × 235 g ÷ expected emergence of 88 comes to 227 kg/ha.
A worked example
| Step | Value |
|---|---|
| Target stand | 250 plants/m², the hard red spring wheat figure in the Alberta table |
| Thousand kernel weight | 35 g, the figure Alberta uses in its own wheat example |
| Seedling survival | 0.85, inside the 0.80 to 0.90 range Alberta suggests for cereals |
| Seed rate | 250 × 35 ÷ 0.85 ÷ 100 = 103 kg/ha |
| If the lot is 98 pure by weight | 103 ÷ 0.98 = 105 kg/ha |
Alberta works its own example in imperial units: a low-end wheat target of 16 plants per square foot, 35 g and survival 0.90 give 60 lb/acre.
Target plant densities by crop
These are the target stands Alberta Agriculture lists from multi-year trials in its prairie conditions. Use them to see the shape of the numbers, then replace them with the guide of your own country or region.
| Crop | Target plants per m² | Note from the source |
|---|---|---|
| Hard red spring wheat | 250 | Range 16 to 30 plants per square foot |
| Durum | 210 | Range 16 to 24 per square foot |
| Barley, two-row | 210 | Range 16 to 30 per square foot |
| Oats | 250 | Range 16 to 30 per square foot |
| Fall rye | 250 | Range 16 to 25 per square foot |
| Field pea | 75 | Range 7 to 9 per square foot |
| Canola, Argentine type | 40 to 60 | Thousand kernel weight 2.5 to 5.5 g, by open-pollinated, synthetic or hybrid type |
| Flax | 300 to 400 | Thousand kernel weight 5 to 6.5 g |
Germination is not field survival
A laboratory germination test counts seeds that sprout in good conditions. In the field some die as seedlings from disease, insects, fertiliser in the seed row, wrong depth, frost or drought. Alberta Agriculture puts cereal seedling loss at roughly 5 to 20 of every 100 germinated seeds, and canola at 30 to 60. Manitoba Agriculture counts on about 95 germination in normal conditions and 90 to 93 in cold, wet soil, because some viable seed in cold soil does not produce a plant. Keep your own emergence counts so the estimate becomes yours.
Before you set the drill
- Use the lot, not the catalogue. Seed size changes between lots and years, so weigh your own seed. See the thousand seed weight guide.
- Work out a low and a high rate. Alberta suggests calculating both ends of the target range, then calibrating the drill to fall between them.
- Read the crop in detail. Wheat has its own page: wheat seeding rate.
How this works in Planva
- Seed catalogue. Reproduction, germination, thousand seed weight, maturity group, purity and tillering for each seed.
- Agroplan. Sowing profiles hold seed by rate or quantity, with plan and actual side by side.
- Field history. Each field shows its operations with planned and actual rates.
Planva records the numbers you decide on. It does not choose the rate. See plan versus actual for how a rate is checked against the work done.
Sources
Common questions
Multiply the number of millions of viable seeds you want per hectare by the thousand seed weight in grams and by 100, then divide by the sowing value of the lot. The result is in kg/ha. Sowing value is germination times purity divided by 100.
The real Planva interface, shown with test data.
