Seed Rate Calculator
Find how much seed to buy for an area from spacing, germination rate and seed weight.
About the Seed Rate Calculator
Enter the area, row and plant spacing, seeds per hill, germination rate and thousand-seed weight. The calculator gives the plant population and the weight of seed to buy.
Target plant population = area ÷ (row spacing × plant spacing). Divide by the germination rate (from the seed tag) to allow for seeds that don't come up, then convert to weight using the thousand-seed weight. Add more in poor seedbeds or when sowing late.
The formula
Seed (kg/ha) = plants per ha ÷ germination × TSW ÷ 10⁶
Worked example
1 hectare at 22.5 × 10 cm spacing, 85% germination, 40 g per 1,000 seeds
- Plants: 10,000 m² ÷ (0.225 × 0.1) = 444,444
- Seeds: 444,444 ÷ 0.85 = 522,876
- Seed: 20.9 kg
Questions people ask
What's thousand-seed weight?
The weight in grams of 1,000 seeds; it varies by variety and lot.
Should I add extra for field losses?
Often 5–10% for pests and poor emergence.