Fit, Sizing & Packing Questions, Answered
32 researched, fact-checked answers to the questions hikers ask most about fit, sizing & packing.
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In plain English
Getting a pack to fit is like getting shoes to fit. First you measure, then you try it on with real weight inside, then you adjust. The main measurement is your back length, from the bump at the base of your neck to the top of your hip bones. The second is around your hips, where the padded belt will sit.
Once the pack is on, you tighten the straps in order, starting with the hip belt. The hip belt is the foundation, like the bottom row of bricks in a wall. If it is loose or in the wrong spot, everything above it ends up leaning on your shoulders, and your shoulders start to ache.
Packing is about balance. Heavy things like food and water go close to your back, roughly in the middle. Light, squashy things like a sleeping bag go at the bottom. And the less the whole pack weighs, the easier every mile feels.
Measuring torso and hips: where brands agree and differ
The torso method is close to universal: C7 vertebra to the iliac crest.9,10 Gregory finds C7 by tilting the head forward and feeling for the bump, and Granite Gear finds the crest by putting hands on the hips with thumbs pointing across the back.9,2 Mystery Ranch is the outlier, measuring to a point just behind the belly button, and it recommends sizing down when you fall between sizes, which matches the between-sizes answer here.11
Hip measurement is less settled. The answer here says to measure at the iliac crest, not the waistline, which matches Gossamer Gear's method.12 But Granite Gear says hip-belt size is roughly your regular pant waist, ULA sizes men's belts at pant waist plus 2 inches, and Mystery Ranch measures just above the hip bones.2,3,11 Use the method on the brand's own chart.
The 20% rule and what the evidence says
Several answers give 20% of body weight for multi-day loads and 10–15% for day hikes. No primary source for the 20% figure was found; it is a hiking-community rule of thumb. Deuter, a pack maker, says people can carry a maximum of 20–25%.13 A 2022 research review says adult loads in military, hiking and mountaineering settings should generally stay under 40%.5 A 2026 study of long-distance hikers found forefoot pressure rose 5.41% with a 10% load and 8.73% with a 20% load, with a clear rise above about 10%.4 US Army doctrine sets about 30% for a fighting load and 45% for an approach march.14 In practice, Appalachian Trail hikers in one study carried about 25% (men) and 28% (women).15
Whatever the percentage, every kilogram costs energy. One lab study measured about 7.6 W of extra metabolic power per extra kilogram carried.16 Weight on the feet costs far more: each kilogram added to the foot raises energy use by 7–10%.7
Where heavy items go, including the bear canister
The AMC puts dense items about two-thirds of the way up the main compartment, centered against the back; Deuter says shoulder height, close to the back; WTA says on top of the sleeping bag, close to the spine.6,13,17 US Army doctrine says packing heavier items higher and closer to the body can cut marching energy cost by as much as 25%.14 One military review adds a caveat: low or mid-back placement may suit uneven terrain.7 The core-zone advice here, between the shoulder blades and hips, sits in the middle of that range.
At camp, a canister only works closed and locked, on flat ground at least 100 feet from camp and away from cliffs or water.18 Some parks ask for more; Rocky Mountain requires 200 feet.19