My shoulders screamed by mile four. The hipbelt rode three inches above my hips. By mile eight, I couldn't lift my arms above my head.
Backpack sizing has nothing to do with your height. I learned this after spending $340 on a 65-liter pack that destroyed my shoulders because I measured wrong. The outdoor industry sizes packs by torso length, not overall height. A 6'2" person with a short torso needs a small pack. A 5'6" person with a long torso needs a large. Miss this measurement and you'll carry weight on your shoulders instead of your hips, turning every hike into orthopedic torture.
I made three catastrophic sizing mistakes in four months. Bought based on height, chose capacity based on "what if" scenarios, and ignored that empty packs fit everyone. Here's exactly why most people get pack sizing completely wrong and how understanding two measurements changed everything.
The Height Mistake That Started Everything
March 2023. I decided backpacking was my new hobby.
I walked into REI ready to buy gear. Told the salesperson I'm 5'10" and needed a pack for weekend trips. He showed me their medium and large packs. Said large fits people 5'9" and taller.
I'm 5'10". I bought the large. Seemed obvious.
First trip was 11 miles near Lake Tahoe. Loaded the pack with 35 pounds of gear. Within two miles, my shoulders burned. The hipbelt sat wrong. All the weight crushed my trapezius muscles.
I assumed I packed wrong or wasn't strong enough. Adjusted the straps twenty different ways. Nothing helped.
By mile eight, I had shooting pain down both arms. We made camp and I could barely lift the tent poles. My girlfriend carried my pack the last mile back to the trailhead.
At home, I researched proper fit. Discovered I'd measured nothing. Just bought "large" because I'm not short.
Turns out my torso measures 17 inches. Large packs fit 19-21 inch torsos. I needed a medium. The pack literally didn't fit my body.
The Capacity Disaster Three Weeks Later
April 2023. I understood torso length now. Bought a proper medium pack.
But which capacity? The REI salesperson asked about trip length. I said mostly weekends, maybe someday a week-long trek. He suggested 50-65 liters.
"Get the bigger one," he said. "You'll grow into it. Better to have extra space."
I bought 65 liters. Cost $340. Seemed smart to plan for the future.
May 2023. Three-day trip near Yosemite. My base weight was 18 pounds plus three days of food. Total around 25 pounds.
I packed everything into my 65-liter pack. It looked half empty. I added extra clothes, camp shoes, a book, a backup fleece, extra fuel canisters. Why not? I had the space.
My pack now weighed 38 pounds. I'd filled the capacity because it existed.
Mile five felt okay. Mile ten was brutal. By mile fifteen, every step hurt. My hips ached. My lower back seized.
At camp, I unpacked and realized half my gear was "just in case" junk. The backup fleece I never wore. Camp shoes I used for fifteen minutes. The book I was too tired to read.
Big packs encourage overpacking. It's not willpower. It's physics. Empty space demands to be filled.
The Final Lesson In September
September 2023. I'd learned torso length and capacity the hard way.
But I still didn't understand weight distribution. Thought a well-fitting pack meant comfortable shoulders. Wrong.
I measured my torso correctly at 17 inches. Bought a 45-liter pack sized medium. Packed only essentials for a four-day trip. Total weight: 28 pounds.
First morning felt amazing. The pack sat perfectly. No shoulder pain. Then I hiked uphill for three hours.
By lunch, my shoulders hurt again. Not as bad as before, but still wrong. My hips felt fine. The weight was all on my upper body.
I stopped and watched other hikers pass. Their packs sat differently. Lower on their backs. Hipbelts actually on their hips, not their waists.
I'd been wearing my pack too high. The bottom of the pack should align with your hip bones. Mine sat three inches higher because I thought "high and tight" meant better.
Loosened everything and repositioned. The hipbelt dropped to actually rest on my iliac crest. Retightened the shoulder straps with just finger pressure instead of pulling hard.
The difference felt like dropping twenty pounds. Suddenly 80% of weight rode my hips instead of my shoulders.
Proper fit isn't intuitive. It requires specific measurements and adjustment techniques most people never learn.
Here's what pack sizing actually requires:
Torso Length Is The Only Measurement That Matters For Size
Your height means nothing for pack sizing. Two people standing 5'8" can have completely different torso measurements. One needs small, the other needs large.
Measure from your C7 vertebra to your iliac crest. C7 is the bony bump at the base of your neck when you tilt your head forward. Iliac crest is the top of your hip bones. That distance is your torso length.
Small packs fit 15-17 inch torsos. Medium fits 17-19 inches. Large fits 19-21 inches. These ranges vary by manufacturer, but the concept stays consistent.
REI's testing confirms 80% of pack fit problems come from incorrect torso measurement. Outdoor Gear Lab found people consistently buy one size too large by using height instead of torso length.
Why it works: Packs transfer weight to your hips through the hipbelt. The hipbelt must align with your iliac crest. Torso length determines where the hipbelt sits on your body. Wrong torso size means the hipbelt can't reach your hips regardless of adjustment.
Capacity Should Match Actual Trips Not Hypothetical Adventures
Weekend backpacking needs 40-50 liters maximum. Three to five-day trips need 50-60 liters. Week-long expeditions need 60-70 liters. Buying bigger "just in case" guarantees overpacking.
Every backpacker I know who bought 65+ liters for weekend trips regrets it. Large capacity creates a gravitational pull toward unnecessary gear. You'll pack the backup everything because space exists.
Switchback Travel's data shows experienced backpackers average 15-18 pound base weights in 45-50 liter packs. Beginners average 25-30 pounds in 60-70 liter packs carrying the same trip length.
Why it works: Constraints force efficiency. A 45-liter pack physically prevents overpacking. A 70-liter pack enables it. Choose the smallest capacity that fits your actual needs, not your imagined future needs.
Hipbelts Carry 80% Of Weight If Positioned Correctly
The hipbelt must rest on your iliac crest, not your waist. Your iliac crest is the bony shelf at the top of your hips. Find it by placing your hands on your hips and sliding up until you feel bone.
Position the center of the hipbelt padding directly on this bone. Then tighten firmly. The hipbelt should be snug enough that you can barely slide two fingers between the belt and your body.
Shoulder straps should have minimal tension. You should be able to slide your hand between the strap and your shoulder with light resistance. Most people overtighten shoulder straps, which defeats the hipbelt's purpose.
Backpacking Light's research shows proper hipbelt positioning reduces shoulder strain by 75% and extends comfortable hiking distance by 40%. Your legs are stronger than your shoulders. Use them.
Why it works: Your skeletal system carries load better than your muscular system. Hips transfer weight to your leg bones. Shoulders transfer weight to muscles. Bones don't fatigue. Muscles do.
Empty Packs Fit Everyone Perfectly Until You Add Weight
Never judge pack fit empty. Every pack feels comfortable with zero weight. Load it with 25-30 pounds before evaluating fit.
Bring weight to the store when trying packs. Use water bottles, books, whatever adds real mass. Walk around for fifteen minutes minimum. Go up and down stairs if possible.
Gregory's fitting guide specifies testing packs with weight that matches your expected load. Osprey's research shows 65% of returns come from people who tested empty packs and discovered fit problems on trail.
Why it works: Weight changes everything. Shoulder straps that feel perfect empty dig into your collarbone under load. Hipbelts that seem fine empty ride up or slip down when carrying weight. Real-world testing eliminates guesswork.
Adjustable Suspension Systems Accommodate Growth And Sharing
Many packs feature adjustable torso lengths. Velcro systems or sliding panels let you modify the pack to fit different torso sizes within a 2-4 inch range.
This matters for growing teenagers, couples sharing gear, or people between sizes. A medium pack with adjustable suspension can fit 16-20 inch torsos instead of just 17-19.
The trade-off: Adjustable systems add 4-8 ounces versus fixed suspension. For some people, the versatility justifies the weight penalty. For others, buying the correct fixed size works better.
REI's Trailmade series offers 4-inch adjustable torso ranges. Granite Gear's systems adjust both torso length and hipbelt circumference independently. This precision eliminates the "almost fits" problem.
Why it works: Bodies change. Teenagers grow. People lose weight. Couples share expensive gear. Adjustable suspension means one pack serves multiple needs without compromising fit for anyone.
I wasted $680 and three painful trips learning that height doesn't determine pack size, big capacity encourages overpacking, and proper fit requires loading weight before judging comfort. Now I measure torso length accurately, buy the smallest capacity that fits my actual trip length, test every pack with 30 pounds before purchasing, position my hipbelt on my iliac crest instead of my waist, and verify shoulder straps carry minimal weight.
My current pack: 45 liters, medium torso, fits my 17-inch measurement perfectly, carries 25 pounds comfortably for four days, cost $240. The difference wasn't spending less. The difference was finally understanding the two measurements that actually matter.