Compression Spring Rate Calculator
Calculate the spring rate, force at a given deflection and solid height of a round-wire helical compression spring. Implements k = G * d^4 / (8 * D^3 * n) with a Wahl curvature correction available for stress estimates.
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How to use this calculator
- Enter wire diameter d, mean coil diameter D and number of active coils n.
- Select the material to set the shear modulus G, or enter G directly.
- Enter a working deflection to get the force at that deflection and the solid height check.
Frequently asked questions
What is the difference between mean coil diameter and outer diameter?
Mean coil diameter D is measured to the centre of the wire. Outer diameter equals D + d and inner diameter equals D - d. Spring formulas use the mean diameter.
How many active coils does my spring have?
Active coils are the coils free to deflect. For closed and ground end compression springs, subtract roughly two coils from the total coil count.
Which shear modulus should I use?
Music wire is about 79.3 GPa, stainless steel 302 about 69 GPa, chrome silicon about 79.3 GPa and phosphor bronze about 41 GPa.