Torsion-spring IPPT calculator.
Three measurements — length, wire diameter, inside diameter — gives you inch-pounds per turn instantly. Same formula Service Spring and IDA publish. Matches their charts.
How it works:IPPT = (wire⁴ × 33,128,000) ÷ (10.8 × N × Dm), where N = floor(length ÷ wire) — total integer coils — and Dm = ID + wire (mean diameter). 33,128,000 is calibrated against Service Spring's calculator, the industry standard reference.
Measure wire with calipers across the wire itself, not the coil. Measure ID across the inside of the coil (not the outside — that’s OD). Spring length is at rest with all coils touching, no stretch.
0.207, 0.218, 0.225, 0.234, 0.243, 0.250, 0.262, 0.273, 0.283, 0.295, 0.307, 0.313, 0.331, 0.343, 0.375 are the workhorse sizes. Type any decimal — the box accepts custom too.
Inch-pounds of torque per full turn of the spring. Multiply by the number of turns you wind to get total holding torque. That divided by drum radius tells you how much weight the spring lifts.
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