Calculate optimal sowing rates based on TGW and field conditions.
Recommended Seed Rate:0 kg/ha
Seeds per Square Meter:0 seeds/m²
Total Establishment Rate:0%
function calculateSeedRate() {
// Clear previous results and errors
document.getElementById('errorDisplay').style.display = 'none';
document.getElementById('resultsDisplay').style.display = 'none';
// Get Input Values
var target = parseFloat(document.getElementById('targetPopulation').value);
var tgw = parseFloat(document.getElementById('tgw').value);
var germination = parseFloat(document.getElementById('germination').value);
var emergence = parseFloat(document.getElementById('emergence').value);
// Validation
if (isNaN(target) || target <= 0) {
showError("Please enter a valid Target Plant Population.");
return;
}
if (isNaN(tgw) || tgw <= 0) {
showError("Please enter a valid Thousand Grain Weight (TGW).");
return;
}
if (isNaN(germination) || germination 100) {
showError("Please enter a valid Germination percentage (1-100).");
return;
}
if (isNaN(emergence) || emergence 100) {
showError("Please enter a valid Expected Emergence percentage (1-100).");
return;
}
// Calculation Logic
// Formula: Rate (kg/ha) = (Target Plants/m² * TGW) / (Establishment % as decimal * 100)
// Or strictly: (Target * TGW * 100) / (Germination * Emergence)
// 1. Calculate Combined Establishment Rate (decimal)
var establishmentDecimal = (germination / 100) * (emergence / 100);
// 2. Calculate actual seeds needed per m² to achieve target
var seedsNeededPerM2 = target / establishmentDecimal;
// 3. Calculate weight per m² in grams (seedsNeeded * weight of 1 seed)
// Weight of 1 seed = TGW / 1000
var weightPerM2g = seedsNeededPerM2 * (tgw / 1000);
// 4. Convert g/m² to kg/ha
// 1 g/m² = 10 kg/ha
var seedRateKgHa = weightPerM2g * 10;
// Display Results
document.getElementById('resKgHa').innerHTML = seedRateKgHa.toFixed(2) + " kg/ha";
document.getElementById('resSeedsM2').innerHTML = Math.ceil(seedsNeededPerM2) + " seeds/m²";
document.getElementById('resEstablishment').innerHTML = (establishmentDecimal * 100).toFixed(1) + "%";
document.getElementById('resultsDisplay').style.display = 'block';
}
function showError(message) {
var errDiv = document.getElementById('errorDisplay');
errDiv.innerHTML = message;
errDiv.style.display = 'block';
}
Understanding the Seed Rate Calculator Formula
Calculating the correct seed rate is one of the most fundamental steps in agronomy to ensure high yield potential. Planting too thinly wastes land potential and invites weeds, while planting too densely increases competition for light, water, and nutrients, leading to disease pressure and lodging.
This calculator uses the standard agricultural formula to convert your target plant population into a specific weight of seed required per hectare (kg/ha).
The Mathematical Formula
The calculation performed by this tool is based on the following standard equation:
Where Establishment % is the product of your Germination rate and your expected Field Emergence.
Key Input Factors Explained
1. Target Plant Population (Plants/m²)
This is your agronomic goal. It varies significantly by crop type, sowing date, and local climate. For example, winter wheat might target 200–275 plants/m² for early sowing, rising to 350+ plants/m² for late sowing. Check your local agronomy guides for the optimal target.
2. Thousand Grain Weight (TGW)
TGW represents the weight of 1,000 seeds in grams. This is the most variable factor between different seed lots. A variety with large seeds (e.g., TGW of 52g) requires a much higher sowing weight (kg/ha) to achieve the same number of plants as a small-seeded lot (e.g., TGW of 38g).
3. Germination (%)
This value is typically found on the seed certification tag or lab analysis. It represents the percentage of seeds that are viable under ideal laboratory conditions. Standard certified seed is usually above 90% or 95%.
4. Field Emergence (%)
This is an estimate of how many viable seeds will actually survive the soil conditions to become established plants. This factor accounts for:
Seedbed quality (cloddy vs. fine)
Soil moisture and temperature
Pest pressure (slugs, birds)
Sowing depth accuracy
In perfect conditions, emergence might be 90-95%, but in poor, wet, or late conditions, it can drop to 60-70%.
Why Not Just Sow by Weight?
Historically, farmers often sowed a flat rate (e.g., 150 kg/ha) regardless of seed size. However, because seed size (TGW) varies, this approach leads to inconsistent plant populations. By using the Seed Rate Calculator Formula, you sow based on the number of seeds, not just their weight, ensuring your crop starts with the optimal density for maximum yield.