To determine your torso length, measure the difference in height between the top of your hipbone to the mid-point of each shoulder. You can do this yourself, as follows:
Stand with your back against a wall with a hard covered book and pencil in hand. Place the book vertically against your sides with the bottom edge of the book resting on top of your hipbone and the back edge against the wall. Mark the height of the lower edge of the book on the wall. This is the height of the top of your hips.
Now place the book vertically by the side of your head, with the back edge resting against the wall and the bottom edge resting on the mid point of one shoulder (half way between your neck and the end of your shoulder- this is where the center of the shoulder straps should lie). Mark the height of the bottom edge of the book on the wall. This is the height of your shoulders.
Now measure the difference in height between the 2 marks on the wall- this is your torso length.
If your Torso Length is less than 38 cm, choose the short (S) torso length. If it is more than 40 cm, choose the long (L) torso length. For 38-40cm either torso length will fit.