Don't get confused, every brand, outdoor shop and expert inter change the following terminologies.

The following One Planet references may help.

Back length. Your back length needs to be matched to a suitable pack frame length; we refer to our frames as short, med, long

Harness size. One Planet have 4 harness sizes to match your body shape and size.

Shoulder strap adjustment. Adjusts the distance between the shoulders and the hips within the confines of the frames length.

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

As a general rule most women have either a short or medium and men a medium or long back length.
It can be difficult to measure your back length accurately, therefore it is best to have a One Planet pack fitted by a One Planet dealer.

Harness Sizes
(Hip belt and shoulder straps)
One Planet packs are available in four harness sizes to accommodate people with different body shapes. The four harness sizes offered will fit most people but custom fitting is available should it be required.
The sizes offered are:
Women's Short
Women's Medium
Universal Medium
Universal Long