Overhead Door Spring Calculator

Overhead Door Spring Calculator

Calculation Results

Turns Required:

Total IPPT:

IPPT Per Spring:

Moment Arm:

Note: Proper spring selection also requires wire gauge and length calculations based on your specific IPPT results.

function calculateSpring() { var weight = parseFloat(document.getElementById('doorWeight').value); var height = parseFloat(document.getElementById('doorHeight').value); var drumDia = parseFloat(document.getElementById('drumDiameter').value); var springs = parseInt(document.getElementById('springCount').value); if (isNaN(weight) || isNaN(height) || weight <= 0 || height <= 0) { alert("Please enter valid positive numbers for weight and height."); return; } // Calculation logic // 1. Calculate turns based on door height and drum circumference // Formula: Turns = (Height in Inches / Circumference) + 0.5 (dead turn) var circumference = Math.PI * drumDia; var heightInches = height * 12; var turns = (heightInches / circumference) + 0.5; // 2. Calculate Moment Arm (Radius of drum) var momentArm = drumDia / 2; // 3. Calculate IPPT (Inch-Pounds Per Turn) // IPPT = (Weight * Radius) / Turns var totalIPPT = (weight * momentArm) / turns; var perSpringIPPT = totalIPPT / springs; // Display results document.getElementById('turnsOutput').innerText = turns.toFixed(2); document.getElementById('ipptOutput').innerText = totalIPPT.toFixed(2); document.getElementById('perSpringOutput').innerText = perSpringIPPT.toFixed(2); document.getElementById('momentArmOutput').innerText = momentArm.toFixed(2) + " in"; document.getElementById('springResults').style.display = 'block'; }

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Understanding Garage Door Spring Math

Calculating the correct spring for an overhead garage door is a critical safety and maintenance task. An improperly sized spring can lead to premature motor failure, snapped cables, or dangerous door drops. This calculator uses the physical properties of your door system to determine the required IPPT (Inch-Pounds Per Turn).

Key Metrics Explained

• Door Weight: This is the dead weight of the door. To measure this accurately, you must disconnect the operator and place the door on a scale while the springs are completely unwound.
• Drum Diameter: Most residential doors use a 4-inch standard lift drum. Larger drums are used for high-lift or vertical-lift configurations and change the leverage applied to the spring.
• IPPT: This stands for Inch-Pounds Per Turn. It represents the amount of torque the spring delivers for every 360-degree rotation. The door is balanced when the total IPPT of the springs matches the door's weight-moment arm ratio.
• Turns: The number of full rotations required to provide enough tension to lift the door from the floor to the fully open position.

Calculation Example

If you have a 150 lb door that is 7 feet tall (84 inches) and you are using a standard 4-inch drum:

1. Circumference: 4″ × π ≈ 12.57″
2. Turns: (84″ / 12.57″) + 0.5 ≈ 7.18 Turns
3. Moment Arm: 4″ / 2 = 2″
4. Total IPPT: (150 lbs × 2″) / 7.18 ≈ 41.78 IPPT

If you use two springs, each spring would need to be rated for 20.89 IPPT.

Safety Warning

Torsion springs are under extreme tension. Replacing or adjusting them without the proper tools (winding bars) and knowledge can result in severe injury or death. Always ensure the door is securely clamped and that you are using the correct wire gauge and length for the calculated IPPT. If you are unsure about the results, consult a professional garage door technician.