Back/Torso length (from hip to shoulder):
XS: 36-41cm
Small: 42-47cm
Medium: 48-52cm
Large/Long: 53-58cm
Small-Medium: 43-51cm
Large-XL: 47-57cm

Depending on the volume of the backpack and its intended use, the suspension system of a backpack becomes a key criterion. Determining back length is not as critical for shorter hikes or everyday backpacks, but is crucial for expedition, trekking and touring backpacks. With these backpacks, the pack weight can only be optimally transferred to the hips if the back length and suspension system are correctly matched.

The centre of the hip belt is ideally located on the hip bones (upper edge of the pelvis) and the sacrum to carry most of the load, especially with large internal frame backpacks. There are exceptions where a shorter backpack length is better, such as in alpine situations, because this allows a shorter overall length of the backpack suspension system to allow easier access to the climbing harness.

To determine the back length, use a tape measure to measure the distance between the base of the shoulders or the level of the 7th cervical vertebra (which you can feel protruding where the neck meets the spine) and the upper edge of the iliac crest.