Free torsion spring calculator from Zigoal. Enter your spring specs to get spring rate, torque, leg tip force and bending stress instantly, in metric or imperial units.
Zigoal Torsion Spring Calculator
Use this torsion spring calculator to estimate spring rate, torque at a given deflection angle, leg tip force, bending stress and inside diameter change for a round-wire helical torsion spring. Enter the wire diameter, mean coil diameter, active coils, leg length and deflection angle — results update instantly as you type, in metric or imperial units.
- Spring rate per 360°
- — N·mm/360°
- Spring rate per degree
- — N·mm/°
Estimated bending stress (% of tensile strength)
Enter valid inputs to see the stress rating.
Inside diameter change
Free: — → Loaded: — mm
Change: — mm
Enter a shaft diameter to check the clearance.
Click or hover an input to highlight it on the diagram, or hover the diagram to find its input.
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The calculator uses the textbook rate formula k = E·d⁴ / (10.8·D·Na) and the bending stress equation with the inside-fibre correction factor Ki, and assumes the spring is loaded in the direction that winds the coils tighter. Treat the results as a design estimate — real springs vary with wire and coil tolerances, arbor friction and leg deflection — and verify critical designs by testing.
How accurate is this torsion spring calculator?
It is accurate for standard round-wire helical torsion springs. The calculator uses the textbook rate formula k = E × d⁴ / (10.8 × D × Na) and the bending stress equation with the inside-fibre correction factor Ki, and it reproduces our reference example (music wire, d = 2 mm, D = 20 mm, 5 active coils, 90° deflection gives 767 N·mm and 15.3 N on a 50 mm leg) to within 1%. Real springs typically differ by a few percent because of wire and coil tolerances, friction against the arbor and leg deflection, so treat the output as a design estimate and test critical springs before production.
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Get a quoteFor the formulas behind the numbers, read our torsion spring force guide.
Working on a different spring type? See all Zigoal spring calculators, or learn more about our custom torsion springs.
