The first step to fitting a backpack is to measure your torso length and waist size. Most stores will measure this for you but this can be done at home as well if you have somebody to help.
How do I measure my Torso Length?
With a soft tape measure, start at the C7 Vertebrae and measure down along the spine to the top of the hip bones, also known as the Iliac Crest. The C7 vertebrae can seen protruding when you tilt your head down slightly. If you are having trouble finding your Iliac crest, put your hands on your hips and press your thumbs in. You should be able to feel the top of your hip bones.
Next, pay close attention to your load distribution inside your pack. This will greatly affect comfort and performance of a backpack. You will want to keep the lighter items on the bottom, heavier items centered next to your back and medium weight items towards the top. Make sure you have time to take this home and load it up with your own equipment. For more detailed information on this, see “How to Pack a Backpack”.
Once you have picked out a pack with the correct torso length and properly loaded it up, it’s time to put your hiking shoes on and go for a test hike. You will want to pay close attention to the following adjustments.
You want this to be snug and wrap around your hips. Most of the weight is transferred to your hips and carried with your legs. You should NOT be feeling any significant weight on your shoulders. You want to make sure these are resting on your hips, not below them.
Again, the shoulder straps should not be carrying much weight. You want to make sure the anchor points(ends attached to the backpack) are at least 1 inch below the top of your shoulders. If these anchor points are too high or extremely low, this indicates improper hip-belt fit or torso length.
Load Lifter Straps
These are the straps connecting the top of the pack to the top of your shoulder straps. The tighter these are pulled, the closer the pack is to your back. You will want to keep these tightened so they form a 45 degree angle. This will keep it the pack perpendicular with your hips. If too tight or loose, you will feel more weight on your shoulders.
On modern packs, manufacturers usually integrate some kind of whistle or strap for small gear. This should be loosely fitted across the sternum if used at all. Over-tightening will disturb the intended fit of the pack.