Calculate optimal seeding rates based on TGW and field conditions
Plants per square meter (m²)
Weight of 1000 seeds in grams (g)
Certified germination percentage (%)
Expected field survival percentage (%)
Please enter valid positive numbers for all fields.
Recommended Seed Rate (Metric):– kg/ha
Recommended Seed Rate (Imperial):– lbs/acre
Total Seeds Required:– million seeds/ha
Effective Establishment:– %
How to Calculate Seed Rate Accurately
Calculating the correct seed rate is one of the most fundamental steps in agronomy to ensure maximum yield potential. Simply planting by weight (e.g., "150 kg per hectare") without accounting for seed size and field conditions often results in stands that are either too thick, leading to lodging and disease, or too thin, inviting weeds and reducing yield.
The Formula
To calculate the seed rate scientifically, you must account for the specific weight of the seeds you are planting and the percentage of seeds expected to establish into viable plants. The standard formula used by agronomists is:
Target Plant Population (Plants/m²): This is your agronomic goal. For winter wheat, this might be 225-275 plants/m² depending on sowing date. For spring barley, it might be higher. Consult your local agronomy guide for the optimal density for your crop and region.
Thousand Grain Weight (TGW): This indicates the size of the seed. TGW varies significantly between varieties and even batches. A batch with a TGW of 50g will require a 25% higher seeding weight than a batch with a TGW of 40g to achieve the same number of plants.
Germination Rate (%): This is found on the certified seed tag. It represents the percentage of seeds that will sprout under ideal laboratory conditions.
Field Emergence (%): Also known as establishment rate. This accounts for field losses due to soil conditions, pests, depth of planting, and seedbed quality. Typical values range from 80% (good conditions) to 60% or lower (poor, cloddy seedbeds).
Example Calculation
Let's look at a realistic scenario for planting winter wheat:
Target: 275 plants/m²
TGW: 48 grams
Germination: 98%
Field Emergence: 85%
First, calculate the total establishment percentage: 0.98 × 0.85 = 83.3%.
Then, apply the formula:
(275 × 48) ÷ 83.3 = 158.5 kg/ha.
If you ignored the TGW and assumed a standard 40g seed size, you might have under-seeded significantly, compromising your final harvest.
Why "Lbs per Acre" Still Matters
While scientific calculations are often done in metric units (kg/ha) due to the easy conversion of TGW (grams), many farmers operate in imperial units. The conversion factor is 0.892. To convert kg/ha to lbs/acre, simply multiply the metric result by 0.892.
function calculateSeedRate() {
// Get input values
var targetPop = parseFloat(document.getElementById('targetPop').value);
var tgw = parseFloat(document.getElementById('tgw').value);
var germination = parseFloat(document.getElementById('germination').value);
var emergence = parseFloat(document.getElementById('emergence').value);
// Get elements for display
var resultsDiv = document.getElementById('results');
var errorMsg = document.getElementById('errorMsg');
// Validation
if (isNaN(targetPop) || isNaN(tgw) || isNaN(germination) || isNaN(emergence) ||
targetPop <= 0 || tgw <= 0 || germination <= 0 || emergence <= 0) {
errorMsg.style.display = 'block';
resultsDiv.style.display = 'none';
return;
}
// Logic
// 1. Calculate Total Establishment Percentage
// If Germination is 95% and Emergence is 85%, effective establishment is 0.95 * 0.85 = 0.8075 (80.75%)
// However, standard formula often treats "Establishment" as the final number.
// We will calculate exact viable seed %: (Germination * Emergence) / 100
var effectiveEstPercent = (germination * emergence) / 100;
// 2. Calculate Seed Rate in kg/ha
// Formula: (Target Plants/m2 * TGW) / Effective Est %
// Example: (250 * 45) / 80.75 = 139.3 kg/ha
var rateKgHa = (targetPop * tgw) / effectiveEstPercent;
// 3. Convert to lbs/acre
// Conversion factor: 1 kg/ha = 0.892179 lbs/acre
var rateLbsAcre = rateKgHa * 0.892179;
// 4. Calculate total seeds per hectare (in millions) for reference
// kg/ha * 1000 = g/ha. g/ha / (TGW/1000) = total seeds
// Simplified: (RateKg * 100) / TGW … wait
// RateKg = Mass. Mass(g) = RateKg * 1000.
// Single seed weight (g) = TGW / 1000.
// Count = (RateKg * 1000) / (TGW / 1000) = RateKg * 1,000,000 / TGW
var totalSeeds = (rateKgHa * 100) / tgw; // Result in Millions roughly?
// Let's re-verify: 139kg. 139,000g. TGW 45g. 139000/45 = 3088 (thousands).
// So 3.088 million seeds.
// Calculation: (rateKgHa * 1000) / tgw = thousands of seeds.
// To get millions: ((rateKgHa * 1000) / tgw) / 1000 = rateKgHa / tgw.
var seedsMillions = rateKgHa / tgw;
// Display Results
document.getElementById('resKgHa').innerText = rateKgHa.toFixed(1) + " kg/ha";
document.getElementById('resLbsAcre').innerText = rateLbsAcre.toFixed(1) + " lbs/acre";
document.getElementById('resTotalSeeds').innerText = seedsMillions.toFixed(2) + " million";
document.getElementById('resEffEst').innerText = effectiveEstPercent.toFixed(1) + "%";
// Show results, hide error
errorMsg.style.display = 'none';
resultsDiv.style.display = 'block';
}