When it comes to properly fitting a backpack, no element is more critical than the waistbelt. You should be carrying the vast majority of the weight (80+%) on your hips and lower body, which makes a good waistbelt fit essential. What should you be looking for? And what can you do to improve fit?
When you're trying on a backpack, loosen up the shoulder straps, put the pack on, and position the waistbelt so that the tops of your hips—the bony knobs of your iliac crest—are in the middle of the waistbelt. Cinch the straps tight and check for fit. The waistbelt should wrap snugly around your hips to evenly distribute weight. With an ideal fit, there should be no gaps anywhere—these will increase pressure at other points on the waistbelt.
Most packs feature waistbelt adjustment straps that can moderately affect the shape and fit. If you have a few minor gaps, tightening or loosening these straps may help you fine-tune the fit appropriately. If you have major gaps, or are unable to close smaller gaps by adjusting the straps, the pack is not right for you.
The size of the waistbelt is also important. The padded section should extend forward a few inches past your iliac crest, so that the most padded portion sits atop the boniest—and most sensitive—part of your waist. Too short and you won't get enough cushion. Too long and the padded portion of the waistbelt will extend across your stomach, digging into your gut when you lean forward or bend over.
Many manufacturers--including Osprey, Gregory, and Arcteryx, among others—give you the option of swapping out the waistbelt for one that's the proper size. (Gregory introduced a new adjustable system this year. Read about it here.)
Everybody's waist is shaped differently. Pack waistbelts are designed to grab the curve of the hip to distribute weight to the lower body. Because women's hip are typically curvier than men's, women's waistbelts are also cut more conically than men's. (If you're a woman without much curve in your hips, a men's style might fit you better.)
If you have no curve in your hips you have a fit challenge. There is simply nothing for the waistbelt to catch. This is my big issue. If I don't address this problem, the waistbelt inevitable scooches downward as I hike, giving me painful bruises and abrasions on my hips, especially around the iliac crest.
To address this, I give myself some "hips" (and extra padding) by tying a fleece jacket around my waist. I neatly fold it about four times so that it provides a nice, flat, even surface against my body for the pack to rest on. This helps considerably in comfort. Plus it means I always have a warm layer accessible whenever I stop to rest on cool days.
“Equipped” is an AMC Outdoors blog, written by Matt Heid.