This is murky territory, full of confusion and jargon, with every brand, outdoor shop and expert using different terminology.

To keep it simple, here’s a guide to One Planet references.

Back length: the length of your back needs to be matched by a pack with a suitable frame length. We refer to our frames as short, medium and long.
Harness fits: the One Planet Exact Fit harness has eight harness fits (four male, four female), while the Midi harness has three (one is a women's fit). The hipbelts and shoulder straps of each are designed to match different body shapes and sizes.
Shoulder strap adjustment: adjusts the distance allowed for between the shoulders and the hips, within the confines of the frame’s length.

Frames
One Planet packs with the Exact Fit and Midi harness systems are available with three frame lengths: short, medium and long. As a general rule, most women have a short or medium back length, while most men have a medium or long back length.

To measure your back length, record the vertical distance from a point level with the crest of your shoulders to your iliac crest (the top of the hip bone).

It can be difficult to measure your back length accurately. To obtain a perfect fit, it is best to have a One Planet pack fitted by a One Planet dealer.