When it comes to getting a backpack that fits comfortably there are something’s that you should be considering.  Certainly you should be considering what you will actually be using it for and the types of weights you will be carrying within it. 

The first that you need to do is measure the length of your torso.  The only real way this can be done is you get a friend to help.

But as well as measuring the length of your torso you need to worry about your waist size.  Certainly most backpacks including the Osprey Atmos 65 come with hip belts which are adjustable and are able to fit different size waists. 

However for women when it comes to getting a backpack that fits comfortably they have now designed ones which come with much narrower shoulder straps as well as having conically shaped hip belts also.