# Spring Index

Written by Jerry Ratzlaff on . Posted in Fastener

Spring index, abbreviated as C, is the ratio between the spring and wire diameter for a helical spring.  A higher spring index has a smaller wire and a larger spring diameter.  A lower spring index has a larger wire and a smaller spring diameter.  The spring index tells how tight a spring's coils are.

### Spring Index Formula

$$\large{ C = \frac{ D }{ d } }$$

Where:

$$\large{ C }$$ = spring index

$$\large{ D }$$ = spring diameter

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

Tags: Equations for Spring