Find Your Torso Length
Whether you're shopping online or in a retail store for a new backpack, you need to know your torso length. Find the C7 vertebrae, which is the largest vertebrae you can feel at the back of your neck. If you tilt your head down you'll easily feel the C7.
Next, find the iliac crest. Your iliac crest is the very top of the hip bone. If you dig your hands into your sides you can feel where the top of the hip bone ends. Follow that point around to the middle of your back. This is the bottom of your torso.
Use a soft tape measure to measure the distance between your C7 vertebrae and your iliac crest. Take that measurement and compare it to the General Backpack Size Guide below. This is a general guide but some manufacturers vary in size so be sure to check the product description for the manufacturer's recommended size.
If you follow the above directions for fitting a backpack, you'll properly find your torso length and the corresponding size backpack that's best for you. Once you have the right-sized backpack you'll need to know how to adjust it properly for a comfortable fit. If you need more information to help you choose the best backpack, check out these additional resources:
How to Adjust a Backpack