This is a size L/XL - I am 5'10" and have a 21" torso (bottom of neck to waist), and it fits perfectly.
It is the 28L model.
The backpack fell on some rocks, and there's a few small tears on one of the bottle holder and outer pocket fabric; see pic for details. But otherwise in great condition.
A nice minimalist hiking, trekking backpack - no longer made by Patagonia.