Spring Rate Calculator
Estimate the stiffness of an ideal helical compression spring from wire diameter, mean coil diameter, active coils, shear modulus, and deflection.
Advanced spring design inputs
Consider preload, solid height, coil pitch, working deflection range, and material presets only after confirming units. A rate-versus-deflection table is linear in this ideal model.
Coil spring rate formula
For a helical compression spring, k = G × d⁴ ÷ (8 × D³ × N). Force is F = k × x and stored energy is E = 0.5 × k × x².
Worked example
With G = 79,000 N/mm², d = 2 mm, D = 20 mm, N = 8, and x = 5 mm, the ideal rate is about 24.69 N/mm and force is about 123.47 N.
Assumptions and limitations
- All inputs must use consistent units; the defaults use N, mm, and N/mm².
- The formula models an ideal compression spring and omits curvature, buckling, end-type, fatigue, and stress correction factors.
- Manufacturer or engineering verification is required for a working spring design.