How to Choose the Right Size Backpacking Backpack?

Choosing the right size backpacking backpack requires measuring your torso length for fit and matching pack volume to your trip length.

For the full breakdown, see our best Backpacking Daypack guide.

Your torso length, not your overall height, determines the fit—and a pack that doesn’t fit correctly will hurt no matter how many liters it holds. The good news is measuring your torso takes about two minutes with a flexible tape measure and a friend. Only after you nail the fit do you match the pack’s capacity in liters to how many nights you’ll be out and what season you’re hiking in.

Why Torso Length Matters More Than Height

Your torso is the distance from the base of your neck to the top of your hip bones, and it varies wildly among people of the same height. A six-foot hiker can have a shorter torso than a 5’8″ hiker, which means they need different pack frames. When a pack’s frame doesn’t match your torso, the load transfer fails. The hip belt sits too high or too low, weight shifts onto your shoulders, and you end up hunched forward to compensate.

Most reputable manufacturers, including Osprey and REI, publish sizing charts that map torso measurements to frame sizes and have detailed fitting guides on their sites. Because there is no industry-wide sizing standard, the same person can wear a medium in one brand and a large in another. Always compare your torso number against the specific pack maker’s chart before you buy. Remember also that women’s packs commonly have shorter torso ranges and differently shaped hip belts than men’s versions.

How To Measure Your Torso And Check The Fit

Grab a flexible tape measure and a friend. The official method from REI’s fitting experts breaks down like this:

1. Tilt your head forward and find the bony bump at the base of your neck—this is your C7 vertebra.
2. Place your hands on your hips with fingers pointing forward, and locate the line across the tops of your hip bones (the iliac crest).
3. Have your friend measure the straight distance from C7 down to that imaginary line across your hip bones. That number is your torso length.

Now check how the pack sits on your body. The hip belt should rest on the top of your hip bones so the load rides on your hips and legs rather than your waist. Shoulder straps should wrap your shoulders comfortably without chafing at the armpits. Tighten the sternum strap to keep the shoulder straps stable, then adjust the load-lifter straps so they pull the pack weight in close to your upper body. When it fits right, you can loosen the shoulder straps partially and the hip belt still carries most of the weight. Most REI stores offer free pack-fitting sessions with a trained specialist if you want a second opinion, and it’s also worth bringing along the gear you plan to carry so you can load it up and test the ride before committing. Osprey’s online size-and-fit wizard walks you through the same measurement process and returns the right frame size for that specific model, which is worth using since sizing charts vary between brands. Reach for a water bottle or squat down with the loaded pack on—if the frame digs into your lower back or the belt slides off your hips, the torso length is off and you need a different size.

Pack Capacity In Liters: Matching Volume To Your Trip

Pack volume is a separate decision from fit. The right number of liters depends on how many nights you’re out, the season, and the bulk of your shelter and sleep system. A summer weekend with a compact down quilt needs far less space than the same two nights in shoulder season with a bulky sleeping bag and extra layers.

These ranges from current retailer guidance are the best starting point:

Day hikes usually fit comfortably in 30 liters, with 40 liters covering winter extras. A weekend trip commonly runs 35 to 50 liters, while 50 to 70 liters handles three to seven nights. Go above 70 liters only for full weeks or winter expeditions. If you want a pack that doubles as airline carry-on, note the common U.S. domestic standard of 22 x 14 x 9 inches; 30 to 35 liters is the safer zone for budget and international airlines.

Common Mistakes To Avoid When Buying

Choosing by height instead of torso length is the most frequent error. Ignoring hip circumference is a close second—a hip belt that’s too small will dig in, while one that’s too large lets the pack sway. Buying by liters alone without considering gear bulk and season leads to an overstuffed pack or one that’s mostly empty. And failing to compare the manufacturer’s own sizing chart wastes the effort of measuring in the first place. If you’re looking for a tested option that carries well on shorter trips, our roundup of the best backpacking daypacks gives you solid picks for the 15–35 liter range.