# Spring Number of Active Coils

Written by Jerry Ratzlaff on . Posted in Fastener

Active coils are the open wound coils exerting energy while under a load of compression, extending, or deflection.  A coil is formed when it is wound one complete 360 degree helix starting with the second coil and count to the second coil on the other end.

### Spring Number of Active coils formula

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

Where:

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

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

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

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

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

Tags: Equations for Spring