Seeding Rate
Enter target plant density, thousand-grain weight and germination rate to compute target plants/ha, seeds/ha and seed rate (kg/ha) for sowing planning and seed purchase.
Input Data
Results
At a glance:Seeding rate is the seed amount to sow per unit area to reach a target stand. Denser sowing than the target is needed because not every seed germinates or survives; seeding rate must account for germination rate and seedling loss. Calculation in three steps: first target plants per hectare = target density (plants/m²) × 10000; then seeds per hectare = target plants ÷ germination rate (the reciprocal of germination corrects for loss — lower germination needs more seeds); finally seed rate (kg/ha) = seeds/ha × thousand-grain weight(g) ÷ 1000000 (convert grams per seed batch to kg/ha). Thus seeding rate rises with target density and thousand-grain weight and falls with germination rate. Accurate seeding controls seedling cost, avoids wasted seed and missing stands, and sets a uniform, competitive canopy.
Formula
Target plants: plants/ha = target density(plants/m²) × 10000.
Seeds/ha: seeds/ha = target plants ÷ (germination% ÷ 100).
Seed rate: seed rate(kg/ha) = seeds/ha × thousand-grain weight(g) ÷ 1000000.
$$N = D_{target} \times 10000$$$$S = \frac{N}{G/100}$$$$R_{kg/ha} = \frac{S \times TGW}{10^6}$$How to Use
- Enter the target plant density (plants/m²) after emergence.
- Enter the seed lot's thousand-grain weight (g) and germination rate (%).
- The tool returns target plants/ha, seeds/ha and seed rate (kg/ha) for purchase and sowing.
Approximate thousand-grain weight (TGW) of common crops
| Crop | TGW (g) | Note |
|---|---|---|
| Wheat | 35–50 | Common bread wheat |
| Rice (paddy) | 20–30 | Variety-dependent |
| Maize | 200–350 | Large seed, high per-seed weight |
| Soybean | 120–200 | Large seed |
| Example: 200/m², 40g, 90% | ≈ 88.9 kg/ha | From case study |
TGW varies by cultivar and year; measure your seed lot for accuracy. Seed rate is seed to sow, not pure live seed — germination already corrects it.
Case Studies
Seed rate for wheat sowing
Target density 200 plants/m², thousand-grain weight 40 g, germination 90%.
Target plants = 200 × 10000 = 2,000,000/ha; seeds/ha = 2,000,000 ÷ 0.90 ≈ 2,222,222.
Seed rate = 2,222,222 × 40 ÷ 1000000 ≈ 88.9 kg/ha — about 89 kg wheat seed per hectare.
Effect of lower germination
Same 200 plants/m² and 40 g, but germination drops to 80%.
Seeds/ha = 2,000,000 ÷ 0.80 = 2,500,000; seed rate = 2,500,000 × 40 ÷ 1000000 = 100 kg/ha.
10-point germination drop needs ~11 kg/ha more seed to keep the stand — shows germination strongly affects seed cost.
FAQ
How to determine the target plant density?
By crop, cultivar, sowing method, soil fertility and management. Agronomic recommendations or trials give the suitable plants/m² after emergence; too dense wastes seed and risks lodging, too sparse lowers yield. Convert to seeds/ha with this calculator after setting density.
What is thousand-grain weight?
The weight of 1000 seeds (g), reflecting seed size and plumpness. Larger seeds (maize, soybean) have high TGW, small seeds (rice, some vegetables) low. It directly scales seed rate: with the same plant count, heavier seeds need more kg/ha. Measure by actually weighing a counted 1000 seeds for accuracy.
Why divide by germination rate?
Because not every sown seed becomes a plant — part fails to germinate or seedlings die. Seeds per hectare = target plants ÷ germination rate: germination below 100 means you must sow more seeds than the target plant count, and the lower the germination, the more seed needed. Field practice often adds a safety factor for soil, pests and weather beyond lab germination.
Should seed rate be live seed or total seed?
The formula's seed rate is the total seed to sow; germination rate already folds in loss, so you enter lab germination and the result is roughly what to spread. If you want pure live-seed basis, divide further by emergence field factor. Use tested germination and true target density for accuracy, and adjust for local conditions.
Does seeding too dense really hurt?
Yes. Excess seed gives too many seedlings, intensifying competition for light, water and nutrients, raising lodging and disease risk and lowering per-plant yield and quality. Sowing by a reasonable target density plus germination correction is most economical and stable — not the more seed the better.
Related Tools
References
Content review: Calculatorism Science Team. Results are for reference only; please refer to the relevant authorities for the official figures.