How to Choose a Backpack | Fit By Torso, Not Height

A backpack must be chosen by torso length rather than height, with the hipbelt carrying 75–80% of the load for comfortable, ergonomic support.

Buying a backpack off the shelf by height or clothing size is the most common mistake — and the one that causes the most trail misery. The real fit starts with your torso measurement, not your T-shirt size. Here is the exact method for picking a pack that carries weight without punishing your shoulders or back.

Step One: Match Capacity to Your Trip

Volume, measured in liters (61 cubic inches equals 1 liter), is the primary spec. Pick capacity by trip length and load weight, not by what looks big enough.

• Day trips and single overnights: 40–50 liters (2,500–3,000 cubic inches). Best for loads under 25 lbs.
• Week-long trips: 75–90 liters (4,500–5,500 cubic inches). Holds up to 50–60 lbs.
• Expeditions and heavy loads: 100+ liters (>6,000 cubic inches). For loads exceeding 60 lbs.
• Travel and college: Roughly 32 liters works for general use, with specific compartments for a laptop and water bottle.

Overbuying capacity is a common trap — a pack larger than needed forces you to carry extra weight and encourages overpacking. List your gear first and estimate total weight before shopping.

Step Two: Measure Your Torso, Not Your Height

Backpack brands size their frames to torso length, which is the distance from the bony bump at the base of your neck (C7 vertebra) down to the vertebra between your hip bones. This measurement has nothing to do with how tall you are. Have a friend help, or ask a local outfitter to do it — most offer free fit assistance.

Once you have that number, match it to the pack’s size chart. The hipbelt must fully cover your hipbones and be snug without restricting your breathing. After you tighten it, the belt should not shift up or drop below the hipbones when you move.

Step Three: Check Shoulder and Load Adjuster Fit

Shoulder straps should lie flat, 1–2 inches (2.5–5 cm) below the top of your shoulders. They should not touch your neck or leave a large gap. The load adjuster straps — the ones connecting the top of the shoulder straps to the pack body — should form a 45-degree angle with your neck.

Step Four: Load It and Walk

Testing a pack empty tells you nothing. Load it with 15–20 lbs of gear or the store’s weighted bags, then wear it for at least 20 minutes. This is the only way to detect chafing, pressure points, or poor weight transfer before you buy.

The hipbelt should bear 75–80% of the total load — your shoulders are there for stability, not for carrying weight. If you feel the straps digging in after five minutes, the fit or the pack design is wrong. Internal frame packs are preferred for backpacking because they pull gear close to your body and distribute weight efficiently. Look for durable, weather-resistant fabrics like high-denier nylon, a molded bottom to hold shape, and a padded hipbelt thick enough for the loads you plan to carry.

If you are shopping for a practical everyday carry or a specialized grocery run, our tested roundup of the best backpack for groceries covers the models that handle weight without tipping over and keep cold items separate. For backcountry use, stick with the torso-fit method above.

Common mistakes are easy to avoid once you know them: never buy by height, never test unweighted, and never exceed a pack’s total carry limit — ultralight packs (designed for 10–30 lbs total) will fail structurally or become painful if you load them like a heavyweight expedition pack (40–70+ lbs). A little feature discipline also helps: less is more on the trail, since extra straps and compartments add weight without utility.