Compression Spring Measurement Guide

5 Compression Spring Dimensions

To measure a compression spring, you can use dial calipers, a micrometer, a ruler or tape measure for larger springs. When measuring a compression spring, you must determine the following five elements:

1. Outer diameter is measured by placing your dial calipers on the outside of the coil’s width.
2. Inner diameter is defined as the width of the inside of a coil spring’s diameter measured from the center of the helix. Sometimes, inner diameter can be difficult to measure accurately. The formula to calculate inner diameter is I.D. = O.D. – 2d where 2d is two wire diameters.
3. Defined as the full length of an uncompressed spring, free length is easy to find. To measure, place your calipers on the full length of the spring.
4. Wire diameter is found by placing your calipers on the wire in the center of your spring.
5. Total coil count is defined as each full rotation and the remainder of the last coil.

As you learn about taking accurate spring dimensions, explore compression spring terminology for helpful symbols and definitions.