Spring Design Calculator
Calculate spring rate, deflection under load, and maximum shear stress (with Wahl correction) for a helical compression spring.
Enter your values
Wire and coil geometry, material, and applied load.
How this calculator works
For a helical compression spring, spring rate (stiffness) is:
G is the wire material's shear modulus, d is wire diameter, D is mean coil diameter, and n is the number of active coils. Deflection under a given force follows directly: δ = F / k. Maximum shear stress in the wire, corrected for coil curvature using the Wahl factor, is:
C = D/d is the spring index. K_w accounts for the higher stress on the inside of the coil compared to the simple torsion estimate.
Typical shear modulus by material
| Material | G (GPa) |
|---|---|
| Music wire / hard-drawn steel | 79 – 81 |
| Stainless steel (302/304) | 69 – 71 |
| Phosphor bronze | 41 – 45 |
Keep the spring index (D/d) between roughly 4 and 12 — outside this range the Wahl correction becomes less accurate and manufacturing gets difficult at the extremes.
Frequently asked questions
What counts as "active" coils?
Active coils exclude the end coils that are ground or squared flat for seating — typically total coils minus 1.5 to 2, depending on the end configuration.
Does this check for buckling or solid height?
No — this covers rate and stress only. Long, slender springs (free length more than about 4× mean diameter) should also be checked for lateral buckling, and solid height should be confirmed to stay within the available installed space.