Field & Seed Inputs
Calculation Results
How to Calculate Seed Rate Per Hectare Formula
Calculating the correct seed rate is one of the most critical steps in agronomy to ensure optimal crop yield. Planting too sparsely results in wasted land potential and weed proliferation, while planting too densely can lead to competition for nutrients, water, and light, causing poor crop development and disease susceptibility.
This calculator uses the standard agronomic formula to determine exactly how many kilograms of seed you need per hectare based on your target plant population and the specific quality of your seed lot.
The Seed Rate Formula
To calculate the seed rate (kg/ha), you need to account for the weight of the seeds and the percentage of seeds that will actually establish a viable plant. The mathematical formula is:
Understanding the Variables
- Target Plant Population (Plants/m²): This is your agronomic goal. For example, wheat might require 200-300 plants/m², while canola might require 40-70 plants/m². Consult local agronomy guides for your specific crop and region.
- Thousand Seed Weight (TSW): This represents the weight of 1,000 seeds in grams. This varies significantly between varieties and seed lots. Large heavy seeds require a higher weight (kg) to achieve the same number of plants compared to small light seeds.
- Germination (%): The percentage of seeds capable of sprouting, usually found on the seed analysis tag.
- Purity/Establishment (%): This accounts for inert matter (dirt, chaff) and expected field losses. Even if germination is 100%, field conditions (pests, soil crusting) might reduce establishment. A common default is 90-95% for purity or anticipated field emergence.
Example Calculation
Let's say you are planting Winter Wheat. Your inputs are:
- Target Population: 250 plants/m²
- TSW (Thousand Seed Weight): 42 grams
- Germination: 95%
- Purity/Field Establishment: 90%
Step 1: Multiply Target Density by TSW by 100.
250 × 42 × 100 = 1,050,000
Step 2: Multiply Germination by Purity.
95 × 90 = 8,550
Step 3: Divide the result of Step 1 by Step 2.
1,050,000 / 8,550 = 122.8 kg/ha
You would set your seeder to distribute approximately 123 kg of seed per hectare.
Why TSW Matters
Many farmers plant by weight (e.g., "100 kg per hectare") rather than by seed count. However, if your seed lot has a low TSW (small seeds), planting 100kg might result in overcrowding. Conversely, if the seeds are large (high TSW), 100kg might result in a stand that is too thin. Always adjust your rate based on the specific TSW of the batch you are planting.