Locate your C7 cervical vertebra. Working down your neck, it's the highest vertebra that you can feel protruding near the base of your neck. No need to press hard, you should feel it easily through your skin. This point is usually a bit higher than your shoulders.
Its easier if someone helps you with this step. Measure vertically from your C7 to the floor in cm. Alternatively, mark the height off accurately against a wall or door frame with a piece of removable tape.
Find your Iliac crest. That's the highest point of the top of you hip bone at tde side. Make sure you are not taking the front of your hip bone.
Measure vertically from your Iliac crest to the floor in cm. Alternatively, mark the height off accurately against a wall or door frame with a piece of removable tape.
Work out the difference between the two heights in cm. This is your Macpac back length. It is typically between 32 and 44cm for women, and between 37 and 54cm for men.