Seed Rate Calculator
Seed Rate Starts With How Many Plants You Actually Want
Seeding rate isn't set directly — it's derived backward from the target plant population, the physical size (weight) of the seed being planted, and how much of what you sow will actually germinate and grow into a viable plant. Two batches of the same crop variety can need different seeding rates if their germination percentage or seed size differs, which is why relying on a fixed rate per bag rather than calculating from actual seed lot data risks a stand that's too thin or unnecessarily thick.
The Formula
Seed Rate (kg/ha) = (Plant Population × 1000-Seed Weight g) ÷ (100 × Germination% × Purity%)
Where This Calculation Matters
- Adjusting for a new seed lot — germination percentage and 1000-seed weight both vary lot to lot, so the seed rate for a fresh batch needs recalculating rather than reusing last season's figure.
- Optimizing plant population for yield — too few plants per hectare leaves yield potential on the table; too many creates competition for light, water, and nutrients that also reduces yield.
- Switching row spacing — narrower row spacing (common for weed suppression or specific crops) directly changes the seed rate needed to hit the same target plant population.
- Budgeting seed purchase — an accurate seed rate in kg/ha, multiplied by field area, gives the exact quantity of seed to buy rather than over-ordering as a safety margin.
Worked Examples
| Crop scenario | Plant population | Seed rate |
|---|---|---|
| 20cm row × 5cm plant, 40g/1000 seeds, 90% germ, 98% purity | 100.0 plants/m² | 45.35 kg/ha |
| 75cm row × 20cm plant, 300g/1000 seeds, 95% germ, 99% purity | 6.67 plants/m² | 21.27 kg/ha |
The second scenario reflects a wide-row, large-seeded crop (like corn), which needs far fewer seeds per square meter but a heavier seed rate per plant — the two effects partly offset.
How to Use This Calculator
- Enter row spacing and plant spacing, both in centimeters.
- Enter the 1000-seed weight in grams (from the seed lot's test data).
- Enter the germination rate as a percentage.
- Enter the seed purity as a percentage.
- Select Calculate to get plant population and seed rate in both kg/ha and kg/acre.
Related Calculations
Convert the resulting rate to your actual field size with the Land Area Calculator, or plan the nutrient program with the Fertilizer Calculator.