Free Spring Constant Calculator
Find the spring constant (stiffness) of a helical compression spring from its material and geometry.
Spring Constant (k)
5.139 N/mm
Spring Constant (k) vs Shear Modulus (G)
Helical Spring Constant
The stiffness of a helical compression or extension spring depends on material properties, wire size, and coil geometry.
Formula
k = G d^4 / (8 D^3 Na)
where G is the shear modulus, d is wire diameter, D is mean coil diameter, and Na is the number of active coils. The spring index C = D/d should be between 4 and 12 for practical manufacturability.
Example Calculation
A steel spring with 3 mm wire, 25 mm mean coil diameter, 10 active coils, G = 79.3 GPa.
- 01G = 79,300 MPa (= N/mm^2)
- 02d^4 = 3^4 = 81
- 03D^3 = 25^3 = 15,625
- 04k = 79,300 x 81 / (8 x 15,625 x 10)
- 05k = 6,423,300 / 1,250,000 = 5.139 N/mm
- 06Spring index C = 25/3 = 8.33 (good, within 4-12 range)
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