Wheat Seed Rate Calculator

Wheat Seed Rate Calculator (lbs/acre)

Found on seed tag or by counting/weighing.

Typically 80-90% depending on field conditions.

function calculateWheatSeedRate() { // 1. Get inputs var target = parseFloat(document.getElementById('targetPlants').value); var tkw = parseFloat(document.getElementById('tkw').value); var germ = parseFloat(document.getElementById('germination').value); var emerge = parseFloat(document.getElementById('emergence').value); var resultBox = document.getElementById('calculationResult'); // 2. Validation if (isNaN(target) || target <= 0 || isNaN(tkw) || tkw <= 0 || isNaN(germ) || germ <= 0 || isNaN(emerge) || emerge 100 || emerge > 100) { alert("Germination and Emergence percentages cannot exceed 100."); resultBox.style.display = 'none'; return; } // 3. Calculation Logic // Convert percentages to decimals var germDecimal = germ / 100; var emergeDecimal = emerge / 100; // Calculate total plants needed per acre (43560 sq ft per acre) var plantsPerAcreTarget = target * 43560; // Adjust for germination and emergence to find total seeds needed var totalSeedsNeeded = plantsPerAcreTarget / (germDecimal * emergeDecimal); // Convert total seeds to total grams using TKW var totalGrams = totalSeedsNeeded * (tkw / 1000); // Convert total grams to pounds (453.592 grams per pound) var finalLbsPerAcre = totalGrams / 453.592; // 4. Display Result document.getElementById('finalRate').innerText = finalLbsPerAcre.toFixed(1); resultBox.style.display = 'block'; }

Moving Beyond Bushels Per Acre: Precision Seeding

For decades, many producers seeded wheat based on a fixed volume, such as "2 bushels per acre." While simple, this method fails to account for a critical variable: seed size. Wheat seed size can vary significantly between varieties and growing seasons. Seeding by volume can lead to under-seeding large seeds (reducing yield potential) or over-seeding small seeds (wasting money and increasing disease risk).

To maximize yield potential and stand uniformity, modern agronomy recommends calculating seeding rates based on a Target Plant Population (TPP) and adjusting for the specific Thousand Kernel Weight (TKW) of your seed lot.

Understanding the Calculator Inputs

• Target Plant Population (Plants/sq ft): This is your agronomic goal. It varies by region, planting date, and wheat type. For winter wheat, typical targets range from 30 to 40 plants per square foot. Later planting dates generally require higher target populations.
• Thousand Kernel Weight (TKW in grams): This is the weight of 1000 seeds. It is the most accurate measure of seed size. You can find this on your seed analysis tag or measure it yourself. A high TKW (e.g., 45g) means seeds are large, requiring more pounds per acre to achieve the same plant count as smaller seeds (e.g., 30g TKW).
• Germination Rate (%): Found on the seed tag, this is the percentage of viable seeds expected to sprout under ideal lab conditions.
• Expected Emergence (%): This accounts for "field loss" or mortality. Not every seed that sprouts will become a viable plant due to planting depth, soil crusting, pests, or disease. A common estimate for good conditions is 85-90% emergence. If conditions are poor (cloddy or dry soil), lower this percentage.

Why TKW Matters: A Realistic Example

Imagine two neighbors both aiming for a target population of 32 plants/sq ft. Both have seed with 95% germination and expect 90% emergence.

• Neighbor A (Small Seed): Has seed with a TKW of 30 grams. Using the calculator, their required seeding rate is roughly 112 lbs/acre.
• Neighbor B (Large Seed): Has seed with a TKW of 45 grams. To achieve the exact same stand count, their required seeding rate is roughly 168 lbs/acre.

If Neighbor B seeded at Neighbor A's rate of 112 lbs/acre, their final stand would be significantly thinner than optimal, potentially sacrificing yield. This calculator helps ensure you put the right number of seeds in the ground, regardless of their size.