How to Size and Fit a Backpack So It Rides on Your Hips

For my first couple of Caminos I finished every day with a burning line across the top of both shoulders and a rubbed raw patch where the sternum strap sat. I blamed the pack. So I bought a different pack, a nicer one, and got exactly the same result about four days into the Frances.

The pack was fine. It was the wrong torso size for me, and I was wearing it like a school bag.

The guy who sorted it out worked in a gear shop in Pamplona and spent maybe ten minutes on it, most of which was him filling my pack with weight before he'd touch a single strap. That was the part I'd never done. A backpack isn't a bag you put on your back. It's a system for moving weight off your shoulders and onto the strongest bones you own, and it only works when the frame lines up with your skeleton.

Here's the sequence I use now, on every pack, before every long walk.

Step 1: Measure your torso length, because height means nothing

Pack sizes are not clothing sizes. Small, medium and large refer to your torso length, the distance from the base of your neck to the top of your hips, and it has almost nothing to do with how tall you are. I know 6'2" hikers who wear a small and 5'6" ones who need a medium. Legs vary way more than spines do.

Measuring it takes two minutes and a friend with a soft tape measure. Tilt your head forward and feel for the bony bump at the base of your neck, the C7 vertebra. That's your top point. Now put your hands on your hips with your thumbs pointing back and press in until you feel the shelf of bone across the top of your pelvis, the iliac crest. Draw an imaginary line between your thumbs. Where that line crosses your spine is your bottom point. Measure between the two, standing normally.

Torso length	Pack size
Under 16"	Extra small
16" to 18"	Small
18" to 20"	Medium / regular
20" to 22"	Large
22"+	Extra large

Ranges shift a little by brand, so check the maker's chart. Mine is 19.5", which puts me right on a boundary, and on some packs that means the medium is perfect and on others I want the large with the harness slid down.

Get this wrong and no amount of strap fiddling saves you. A pack that's too short pulls down on your shoulders and parks the hip belt above your hip bones. Too long and the shoulder straps float above your shoulders, the load sways behind you, and the belt slides down onto your thighs. Both feel exactly like "this pack is uncomfortable," which is why so many people buy a second pack instead of a second size.

While you're at it, size the hip belt. ULA's rule is your usual pant waist plus about 2 inches for men, or your narrowest waist measurement plus 3 to 5 inches for women depending on how much your hips flare. When it's buckled you want roughly 4 to 8 inches of gap between the padded wings on either side. If the wings meet in the middle, the belt is too big and the padding is sitting on soft tissue instead of bone.

Step 2: Load the pack before you touch a strap

An empty pack lies to you. It'll feel great on your back in the shop and then behave like a completely different object once there's 9 kg of gear, water and tomorrow's food in it.

Put your real load in it. Not a token amount, and not a maxed-out expedition load either, just whatever you actually plan to carry. For a Camino that's usually around 10% of your body weight, for a mountain trip closer to 20%. If you're still working out what belongs in there, I wrote up how I think about footwear in my Camino shoe guide, and mycaminoguide.com will answer packing questions for a specific route if you'd rather just ask it.

Pack it the way you'd really pack it, too. Heavy items close to your spine and between your shoulder blades, sleeping bag at the bottom, snacks and rain shell up top. Weight sitting far from your back levers the pack backwards no matter how well the harness is adjusted.

Now put it on, loosen everything off, and stand up straight.

Step 3: Hip belt first, and it goes on the bone

The hip belt is the whole point. Done right, it carries about 80% of the load and your shoulders just keep the thing upright.

Center the padded wings over your iliac crest, not around your waist. Most people wear it too high, roughly where a pants belt goes, which drops the load onto your floating ribs and soft belly. The top edge of the belt wants to sit about an inch above the top of your hip bones so the padding cups over that shelf of bone and can't slide down. Pull the two straps out and forward, evenly, until it's snug and secure without crushing you.

Give it a small hop. If the pack stays put, the belt is doing its job.

Step 4: Shoulder straps close to your back, not carrying the load

Now pull the shoulder straps down and back. What you're doing here is pulling the pack in against your back, not lifting it up.

The straps should wrap the curve of your shoulders with no gap along the front of your collarbone, and the anchor point where they attach to the pack should land an inch or two below the top of your shoulders. You want the pack body close enough that it isn't hanging off you and swinging, but not mashed flat against your spine with zero clearance. Snug, in contact, still able to breathe.

The failure mode is cranking these until the pack lifts off your hips. It feels secure for about twenty minutes and then your traps start screaming.

Step 5: Load lifters at 45 degrees

Load lifters are the two short straps running from the top of each shoulder strap to the top of the frame. Their job is to pull the top of the pack in toward you so the weight stays over your center of gravity instead of tipping you backwards.

Tension them until they sit at roughly a 45 degree angle from your shoulder to the frame. Snug, not stiff. Over-tightening them is the second most common mistake after wearing the belt too high, and it pinches the front of your shoulder joint after a few hours.

If you physically can't get anywhere near 45 degrees, that's a sizing signal, not an adjustment problem. A near-flat angle usually means the pack is too long for your torso, a steep one means it's too short.

Step 6: The hand test

This is the one that tells you whether any of the above worked. Slide a flat hand up under a shoulder strap where it crosses your collarbone.

Your hand should slip in with light friction. If it goes in with room to spare, the pack is riding too low or the straps are too loose. If you can't get your fingers in at all, your shoulders are carrying the load and you need to go back to step 3 and get the belt up onto the bone.

Ten seconds, no tools, works on any pack. It's the only check I bother with at the top of a climb when something starts feeling off.

Step 7: Sternum strap, then the stabilizers

Slide the sternum strap so it sits about an inch below your collarbones, then tighten it just enough to stop the shoulder straps sliding outward when you swing your arms. Light tension. It's there to control lateral movement, not to carry weight, and pulling it tight distorts the whole harness and squeezes your chest right when you're breathing hardest.

If your pack has stabilizer straps on the hip belt, running from the belt back to the frame, give them a light tug last. They pull the lower pack body in toward your lumbar and take out the last of the sway.

The full order, every time you put the pack on:

Hip belt
Shoulder straps
Load lifters
Sternum strap
Hip belt stabilizers

Refit on the trail, because the load keeps changing

Your pack at 7am with three liters of water and a full food bag is not the pack you're wearing at 4pm. As it empties, the center of gravity drops and the harness goes slack in places you won't consciously notice. You'll just find yourself getting sore.

Run the sequence again after the first kilometer once everything has settled, and again after lunch. On a long day I'll also shift the load around on purpose, loosening the hip belt a touch for twenty minutes to give my hips a break and let my shoulders take more, then putting it back. Your body appreciates the variety more than it appreciates perfect load transfer for eight straight hours.

None of this is complicated, and none of it requires a better pack. Measure your torso, load the thing before you adjust it, and work the straps from the bottom up. Do that and the pack stops being something you endure and becomes something you forget you're wearing, which is exactly the point.

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