To calculate the amount of rate on a compression spring design based on physical dimensions including material type use the formula provided below:

k = Gd^4 / 8D^3N

Explanation of Symbols:

d = wire size (inches)

D = Mean Diameter (inches)

N = Number of active coils

D / d = Index correction

G = Shear Modulus of Material

k = Spring Constant

G-Value for Common Spring Materials

Music Wire = 11.5 x 10^6

Stainless Steel = 11.2 x 10^6

Phospher Bronze = 5.9 x 10^6

Monel = 9.6 x 10^6

Inconel = 11.5 x 10^6

Copper = 6.5 x 10^6

Beryllium Copper = 6.9 x 10^6

To calculate the amount of spring rate you will need on order to meet your working loads, simply divide the load you will be applying on your spring by the distance you expect your spring to travel or compress under that load. The equivalent to that formula will be your compression spring rate as shown below.

Rate = Load ÷ Travel

k = L ÷ T

Follow these examples to see how the formula works.