The Most Expensive Mistake I've Made (Twice)
I've bought two packs that didn't fit me. The first was a 75-liter behemoth I bought online without trying it on because it was on sale. The torso length was too long for my 18-inch torso, which meant the hipbelt sat on my thighs instead of my iliac crest and every ounce of weight hung from my shoulders. I wore it on one trip — a 3-day loop in the Olympics — and my shoulders were bruised, literally bruised, when I got home. I sold it on r/GearTrade for half what I paid.
The second was a 40-liter ultralight pack I bought because the internet told me I should be ultralight. It was beautiful, weighed 1.5 pounds, and could not comfortably carry my gear. I'm not a true ultralight packer — my base weight hovers around 12-13 pounds — and stuffing 13 pounds of gear plus 3 days of food into a frameless 40-liter pack turned it into an overstuffed sausage that dug into my back. I used it for day hikes for a year before admitting it wasn't the right tool for multi-day trips.
Both mistakes cost me about $200 each after resale losses. Here's how to avoid making them.
Step 1: Determine Your Volume
Pack volume is measured in liters, and choosing the right volume depends on three things: the length of your trips, your base weight, and how compressible your gear is.
20-30 liters: Day hikes. This is your rain jacket, food, water, first aid kit, and extra layer. My day pack is a 22-liter that weighs 1 lb and handles everything I need for a single day on trail.
35-50 liters: Weekend to 3-night trips with a lightweight or ultralight kit. If your base weight is under 12 pounds and your shelter, bag, and pad compress well, a 45-liter pack handles 2-3 nights comfortably. The Osprey Exos 48 (2 lbs 6 oz) is a popular choice in this range — it has a frame and hipbelt for load transfer but keeps weight low through a simplified suspension and lightweight materials.
50-65 liters: The sweet spot for most 3-season backpackers doing 2-5 night trips. My Osprey Atmos AG 65 has been my primary pack for three years, and the 65-liter capacity handles my 12.8-lb base weight plus 4-5 days of food with room to spare. On weekend trips, I compress it down with the side straps and it doesn't feel oversized. On longer trips, I appreciate the extra space.
65-80 liters: Extended trips (5+ days), winter backpacking (bulkier insulation and clothing), or heavier loadouts. The Gregory Baltoro 75 is the comfort king in this range — the A3 suspension system with a fully adjustable hipbelt carries heavy loads better than almost any other pack on the market. If you're carrying 35+ pounds, this is where the Baltoro earns its 4 lb 11 oz weight. The suspension is so good that 40 pounds feels like 30.
Step 2: Get Your Torso Length Right
This is the single most important fit parameter, and it's the one most people get wrong. Your torso length — measured from your C7 vertebra (the bony bump at the base of your neck) to your iliac crest (the top of your hip bones) — determines which pack size fits you, not your overall height. I'm 5'11" with an 18-inch torso, which puts me in a "Medium" in most pack brands. My friend is also 5'11" with a 20-inch torso and wears a "Large" in the same pack. Same height, different fit.
Measure your torso before you shop. Have someone hold a tape measure from the C7 bump on your neck straight down to an imaginary line connecting the tops of your hip bones. Most pack brands publish torso-length ranges for each size: typically 15-17" for Small, 17-19" for Medium, and 19-21" for Large. Some packs, like the Osprey Atmos AG, come in specific sizes. Others, like the Gregory Baltoro, have an adjustable harness that fits a range of torsos — a nice feature if you're between sizes or want to share the pack with a partner.
Step 3: Check the Hipbelt Fit
A good hipbelt wraps around the top of your hip bones and transfers 70-80% of the pack's weight to your legs. When you put on a loaded pack in the store, tighten the hipbelt first — before touching the shoulder straps. The belt should sit centered on your iliac crest with the padding wrapping around the front of your hips. If the belt's padding ends before reaching the front of your hips, it's too small. If the two sides overlap or nearly touch in front, it's too large.
Hip belt pockets matter more than you think. After years of stopping to dig through my pack for my phone or a snack, I now consider hip belt pockets essential, not optional. The Osprey Atmos has generously sized hip belt pockets that fit my phone (with case) and a couple of energy bars. Some ultralight packs skimp on hipbelt pockets or eliminate them entirely to save weight — for me, that's a dealbreaker.
Step 4: Understand Suspension Systems
The suspension is the skeleton of the pack — the frame, back panel, and shoulder harness that determine how weight is carried and distributed.
Framed packs have an internal frame (usually aluminum stays or a plastic framesheet) that transfers weight from the shoulder harness to the hipbelt. This is essential for loads over 20 pounds. The Osprey Atmos AG 65 uses an AntiGravity suspended mesh back panel that creates airspace between the pack body and your back — reducing sweat buildup and improving comfort on hot days. The Gregory Baltoro 75 uses a more traditional foam back panel with a trampoline-style suspension that hugs your back more closely, which some hikers find more stable on rough terrain. Both are excellent; the Osprey runs cooler, the Gregory runs more stable.
Frameless packs rely on the gear inside (typically your sleeping pad folded as a back panel) to provide structure. They're lighter — often under 2 pounds — but they require a carefully organized, tightly packed load to carry well. With a sub-10-pound base weight, a frameless pack like the Gossamer Gear Mariposa (1 lb 9 oz) is a revelation. With a 15-pound base weight, it's a back-aching lesson in why frames exist.
Step 5: Test It Loaded in the Store
Any decent outdoor retailer — REI, local gear shops — will let you load a pack with sandbags or weighted bags to simulate trail weight. Do this. A pack that feels great empty will tell you nothing about how it carries 25 pounds. Load it to your expected trail weight, walk around the store for 15-20 minutes, go up and down stairs if available, and pay attention to pressure points on your hips, shoulders, and lower back.
Adjust everything while loaded: hipbelt tightness, shoulder strap length, load lifter angle (should be about 45 degrees from the top of the shoulder strap to the pack), and sternum strap height (should sit about 1 inch below your collarbones). If you feel any sharp pressure points or the pack shifts when you twist your hips, try a different size or a different pack. No amount of break-in fixes a fundamentally bad fit.
Features That Actually Matter
Water bottle access: Can you reach your side pockets without removing the pack? This sounds trivial, but if you drink from bottles (not a hydration bladder), the ability to reach back and grab a Smartwater bottle while walking saves hundreds of stops over a multi-day trip.
Side compression straps: These cinch the load tight on shorter trips and prevent shifting. The Osprey Atmos has dual side straps that compress the pack body and also secure items in the side pockets.
Trekking pole attachment: If you hike with poles, a dedicated stow system (like Osprey's Stow-on-the-Go) lets you clip and unclip poles without stopping. Without it, you're either holding your poles in one hand while scrambling or stopping to strap them on with bungees.
Removable lid/top pocket: Some packs let you remove the top lid for summit pushes or day hikes from a base camp. The Atmos lid is removable and includes a FlapJacket panel that covers the pack opening when the lid is off. Nice feature, but I've used it maybe twice in three years.
Features That Don't Matter
Built-in rain covers: They blow off in wind, don't cover the bottom of the pack, and add weight. A trash compactor bag ($1, 1 oz) lining the inside of your pack keeps everything dry more reliably than any external rain cover.
Sleeping bag compartments: That zippered bottom compartment with a removable divider? I've never used the divider. The sleeping bag goes in the bottom regardless, and the zipper just adds weight and a potential failure point.
Hydration bladder sleeves: I tried hydration bladders for a year and went back to bottles. Bladders are impossible to dry properly (mold is a real problem), hard to refill without unpacking, and you never know how much water you have left. Bottles are simpler, lighter, and replaceable for $2 at any gas station.
My Recommendation
If you're buying your first backpacking pack for 3-season use, start with the Osprey Atmos AG 65. It fits a wide range of torso lengths across its size range, the AntiGravity suspension carries weight comfortably up to 40 pounds, and the feature set covers everything you need without anything you don't. At 4 lbs 10 oz, it's not ultralight, but it's comfortable and durable enough that most hikers will use it for 5+ years before wanting something different.
If you know you'll be carrying heavy loads or doing extended trips, the Gregory Baltoro 75 carries heavy loads better than any pack I've tried. If you've already dialed your base weight to 10 pounds or under and want a lighter pack, the Osprey Exos 48 or a cottage pack like the ULA Circuit (2 lbs 5 oz) is the next logical step.
Whatever you choose, try it on loaded before you buy it. Your back will thank you at mile 15.
