# Spring Compression Constant

Written by Jerry Ratzlaff on . Posted in Fastener

The constant rate of force expelled by a compression spring per inch or millimeter of travel once a load or force is applied to push and compress the compression spring.

### Spring Compression Constant formula

$$\large{ k_s = \frac {G \; d^4} {8 \; n_a \; D^3} }$$

Where:

$$\large{ k_s }$$ = spring constant

$$\large{ G }$$ = shear modulus of material

$$\large{ d }$$ = wire size

$$\large{ D }$$ = mean coil diameter

$$\large{ n_a }$$ = number of active coils

$$\large{ D/N }$$ = index correction

•  $$\large{ G }$$ value for common spring materials
• Copper = 6.5 x 10^6
• Beryllium Copper = 6.9 x 10^6
• Inconel = 11.5 x 10^6
• Monel = 9.6 x 10^6
• Music Wire = 11.5 x 10^6
• Phospher Bronze = 5.9 x 10^6
• Stainless Steel = 11.2 x 10^6

Tags: Equations for Spring