When I thru-hiked the Appalachian Trail 20 years ago, I knew little about backpacks, and unfortunately the person who sold me one knew even less. I never got the thing to fit properly, and while I hiked the entire trail, I could have—should have—been a lot more comfortable. FIT IS EVERYTHING, and not every pack fits every person. The proper pack makes a 40 lb. load feel like 30, while an ill-fitting or flimsy pack makes that same weight feel like a bag of bricks.
I learned these fit tips through years of fitting and selling backpacks at Eastern Mountain Sports, and they apply to all full-size internal frame backpacks of about 3000 cu. in. or larger.
First, you need to make sure the backpack accommodates your torso length. Your torso length is the distance from your sixth vertebra down to the point of your back that's at the same level as your hip's iliac crest. Sound difficult? It's not. All you need is a flexible cloth tape measure and a helper to find this measurement (or better yet, stop by any Eastern Mountain Sports store and get the help of an experienced pack fitter).
Now, bend your neck forward and feel the top of the spine. The first big vertebra you feel, the one that's poking out at the base of your neck, is the seventh vertebra. Keep your finger on that. Now feel your hip bones. There are two that stick out: one big one down low at the junction of your leg and torso, and the other about 6 in. higher up. This higher hip bone almost feels like a horizontal shelf at your side. That's the iliac crest. Now, poking your other finger on that, trail it along until you reach the center of your spine, at the same level as your iliac crest. The distance between your fingers is your torso length.
Have your helper measure that distance and use that number to narrow your selection of available backpacks based on recommended torso lengths. Many backpacks are adjustable and accommodate a range of lengths. Still other packs come in multiple sizes, each with its own range. Either way, your torso length is a critical piece of information for choosing the right pack for you.
Preparing the Backpack
Place about 15 or 20 lb. of weight in the backpack. Anything will do. Climbing ropes, liters of soda, whatever's at hand. Just make sure the load is evenly distributed in the pack, with some of the weight up high. Also make sure that the shoulder straps, waist belt (also referred to as a hip belt), and load straps are reasonably loose.
Tighten Shoulder Straps
After putting the backpack on, you'll first want to tighten the shoulder straps. This pulls the pack a little higher up on the hips.
Tighten Waist Belt
Cinch the waist belt up nice and snug; not so much that you cut off circulation to your legs, but it will have to be somewhat tight to support the pack's weight. As we will talk about later, your hips should carry the majority of the load.
Waist Belt Positioning
Slip your fingers inside your waist belt and find your iliac crest. The top edge of the waist belt should be about 1 in. above the iliac crest.
Shoulder Strap Positioning
Now look at how the shoulder straps are fitting. If you’re alone, get in front of a mirror and stand sideways. The shoulder straps should be flush with your shoulders and upper back. There should be very little space between the backside of your shoulders and the straps.
Poorly Fitting Suspension
If there’s too much space between the straps and your shoulders, that indicates the backpack’s suspension isn’t matching your torso length, and the distance between the shoulder straps and waist belt needs to be shortened. If the pack’s suspension can’t be shortened far enough, or if the backpack isn’t adjustable, you’ll need to try a shorter model.
If the shoulder straps are wrapping around your shoulders correctly, but the waist belt is positioned too high in relation to the iliac crest, then the distance between shoulder straps and waist belt needs to be increased.
Load Strap Positioning
The load straps attach the top section of the pack to the uppermost portion of the shoulder straps. Ideally, these straps should be at about 45-degree angles, though up to a 15-degree deviation is fine. Pull them to bring the pack a little closer to your body and to keep the load balanced over your hips, but don't yank on the load straps so hard that they cause the front of your shoulder straps to dig in. Play with the adjustments a little to find the sweet spot.
Proper Hiking Posture
Before we check to see where you’re feeling the pack’s weight, lean forward just a little, bending at the hips. This is how you’ll normally carry a backpack. It’s your body’s way of maintaining balance by positioning the load over your own center of gravity (your hips). If you were to rigidly stand straight up, you’d discover that the bottom of the pack presses too much into the lumbar region of your lower back.
Where the Weight Should Fall
If the pack is fitting perfectly, the majority of the weight should be felt in the hip region as opposed to your shoulders. No matter how strong your shoulders are, you don't want all the weight to fall there for hours on end. Your legs are much stronger and can easily support the extra weight of a fully loaded backpack.
Those are the basics of do-it-yourself pack fitting. Always remember that an experienced pack fitter will be able to match you up with the ideal pack and finely tune the suspension to precisely fit your body and make your next hike more enjoyable.