To measure the length of a spring, you will need to first find the equilibrium point of the spring. This is the point where the spring is neither stretched nor compressed. To do this, hang the spring from one end and allow it to hang freely. Once it has come to rest, mark the position of this end of the spring with a piece of tape or a pen. Then, stretch or compress the spring until it reaches its maximum extension or compression. Again, mark this point with tape or a pen. Finally, measure the distance between your two marks to get the total length of the spring.