Spring Index is a commonly stated term when discussing coil spring design and manufacturing. It is a number that correlates the mean diameter and the wire diameter. This number can be used as an indicator to quickly determine how manufacture  able a spring is. In stock spring it can help you understand the coil stiffness or looseness, and how stressed the spring might be.

Spring Index Formula

There is a short formula to follow to calculate a spring’s index. The spring index formula requires that you have the following two measurements: Mean Diameter and Wire Diameter. To know what the mean diameter is, all you need to do is subtract the wire diameter from the outer diameter. You can calculate the spring index yourself or use our Spring Creator Calculator.