Standard 400-8 (2″ Radius)
Standard 5250-10 (2.5″ Radius)
Small Drum (1.5″ Radius)
Single Spring System
Dual Spring System
Required Total IPPT:
IPPT Per Spring:
Estimated Number of Turns:
*IPPT = Inch Pounds Per Turn. Results are estimates based on standard lifting configurations.
Understanding Garage Door Torsion Spring Math
Selecting the correct torsion spring for an overhead garage door is critical for both safety and the longevity of the garage door opener. A perfectly balanced door should feel weightless and stay in place when opened halfway by hand. This calculator helps you determine the IPPT (Inch Pounds Per Turn) required to balance your specific door weight.
How IPPT is Calculated
The physics of a garage door involves balancing the torque of the spring against the weight of the door hanging from the cable drums. The formula used by professional technicians is:
Door Weight: This is the most critical variable. Even a 5lb error can result in an unbalanced door. Always measure with a scale when the springs are disconnected.
Turns: The number of turns is generally the door height in feet plus a "dead turn" (usually 0.5 to 1 turn) to maintain cable tension when the door is open. For a 7-foot door, 7.5 to 8 turns are standard.
Drum Radius: Standard residential drums (400-8) have a 2-inch radius. High-lift or vertical-lift drums will have different configurations.
Example Calculation
Variable
Value
Door Weight
160 lbs
Drum Radius
2 inches
Door Height
7 feet (7.5 Turns)
Calculation
(160 * 2) / 7.5 = 42.67 IPPT
Safety Warning
Warning: Torsion springs are under extreme tension. Replacing or adjusting springs can be dangerous and cause severe injury or death. This calculator is provided for informational and sizing purposes. We recommend all torsion spring repairs be performed by a trained professional overhead door technician.
function calculateTorsionSpecs() {
var weight = parseFloat(document.getElementById('doorWeight').value);
var height = parseFloat(document.getElementById('doorHeight').value);
var radius = parseFloat(document.getElementById('drumRadius').value);
var springCount = parseInt(document.getElementById('springCount').value);
var resultDiv = document.getElementById('torsion-result');
// Validation
if (isNaN(weight) || weight <= 0) {
alert("Please enter a valid door weight.");
return;
}
if (isNaN(height) || height <= 0) {
alert("Please enter a valid door height.");
return;
}
// Logic
// Total Turns = Door Height (in feet) + 0.5 turns for tension
var turns = height + 0.5;
// Required IPPT = (Weight * Radius) / Turns
var totalIppt = (weight * radius) / turns;
var perSpringIppt = totalIppt / springCount;
// Display results
document.getElementById('totalIppt').innerText = totalIppt.toFixed(2);
document.getElementById('perSpringIppt').innerText = perSpringIppt.toFixed(2);
document.getElementById('turnsNeeded').innerText = turns.toFixed(1);
resultDiv.style.display = 'block';
}