Hold the base of the Plastic Compression Springs in one hand, and the calipers in the other hand.
Place the calipers on the outside of the last coil, measuring the largest dimension. This is called the Outside Diameter (O.D.).
Place the calipers on the wire in the center of the spring. This is called the Wire or Material Size. You should also measure the wire toward one end for comparison and accuracy.
Place the calipers on the full length of the uncompressed spring. This is called Free Length.
Count the total coils, beginning at one end, just next to where the wire has been cut. Be sure you count all coils, including any portion of a coil.