How to Count Spring Coils

The active coils are what makes a spring a spring. To count spring coils, it is important to understand what is and is not, an active coil. The active term is generally applied to any portion of a spring that stores and releases energy. In the case of a compression spring, the active portion will expand as the spring is compressed. The opposite is typical of an extension spring. The action of a clutch spring tightening down on a shaft is typical of diameter change as a torsion spring winds up.

When designing a spring and specifying its dimensions, it is critical that the number of coils be counted correctly, as this can have a huge effect on the strength of the spring. Spring end types and end grinding will make a difference in how you count active coils. 

• Open end springs are considered to have virtually no inactive coils. 
• Open end ground springs are considered to have about one-half inactive coils at each end. 
• Closed ends or closed and ground end springs have one inactive coil at each end.

Total number of spring coils are counted from tip to top. To count the spring coils, simply start at one end of the spring, where the wire has been cut, then follow the wire round - every time you go through 360° that counts as a full coil (180° = 1/2 coil, 90° = 1/4 coil etc,). 

How to Count Spring Coils

The compression spring pictured above has five coils (and not six). This same method applies to extension springs and torsion springs.