Hiking Backpack Size Guide: How to Choose the Right Fit

01Volume by Trip Type

Capacity is measured in litres and counts every compartment: the main body, hip pockets, side pockets and any rear mesh. The right amount depends on how long you're out and how much it takes to stay comfortable, not merely safe.

A day hike usually fits in 15–30 L, which holds water, snacks, a layer and first-aid basics. An overnight or weekend trip needs 30–50 L for a sleep system, one change of clothes and camp food. A multi-day trek wants 50–65 L for a full sleep system, several days of food and extra layers. An expedition or winter load pushes past 65 L, because bulkier cold-weather gear and a longer food supply take more room.

Cold is the main exception to those numbers. Insulated layers, a warmer bag and a thicker pad all eat more space than their summer versions, so it's common to jump up one bracket for the same trip length once the temperature drops. Flying with the pack changes the sums too, because airlines limit centimetres and not litres. Our guide to whether a 55 L backpack fits as a carry-on in Canada explains how to check.

02Torso Length Beats Height

Two hikers who both stand 178 cm tall can need completely different frame sizes, because pack sizing is built around torso length, not overall height. A shorter person with a long torso and a taller person with a short one can land on the same frame, and neither would get there from a height chart.

To measure yours, tilt your head forward and find the bony bump where your neck meets your shoulders. That's the top. Then find your iliac crest, the top of your hip bones, roughly level with your belly button from behind. Measure straight down between the two with a flexible tape. That number is your torso length, and it's what most brand size charts (small, medium, large) are built around. Our guide to how a hiking backpack should fit goes through the measuring and then shows how to set the hip belt and every strap in order.

It matters because a pack too long for your torso pushes the hip belt down onto your thighs, where it can't carry weight off your shoulders, while a pack too short rides up and digs the frame into your lower back. Both feel like "the pack doesn't fit", but both are really a torso mismatch, and no amount of strap adjustment fully fixes either.

03Check the Fit Loaded

A pack that feels fine empty on the shop floor can feel like a different pack with 12 to 15 kg inside. Judge fit loaded, because weight is what shows whether the frame and hip belt are doing their job.

• Load it to roughly the weight you'll really carry
• The hip belt sits on top of your hip bones, not your waist
• Most of the load feels like it rests on your hips
• Shoulder straps wrap snugly with no gap or pressure point
• Load-lifter straps sit at roughly 45° from the shoulders
• Walk, bend and twist before you decide

04Fitting Water Into the Plan

Hydration capacity is a separate decision from pack volume, and the two are easy to blur. A 3-litre bladder takes up real space and adds about 3 kg once full, so it belongs in your volume estimate, not treated as free extra.

For a day hike of a few hours, a bottle or a smaller bladder is usually enough, and deciding how much to carry is its own question, covered in our hiking hydration guide. For longer days with few refill points, a dedicated setup earns its space: ARWE's 3L Tactical Hydration Backpack is built around that layout, with the bladder sleeve sized in from the start instead of squeezed into a general-purpose pouch.

05Common Sizing Mistakes

Most fit complaints trace back to a few repeatable mistakes, not a flaw in the pack. The commonest is sizing by height instead of torso, since a height chart is a rough start at best and the torso measurement is what sets the frame. The second is buying the biggest pack "just in case": spare capacity gets filled, and every extra litre is extra weight on your hips for the whole trip, so size for the trips you take most. The third is judging fit empty, which tells you almost nothing about how the hip belt and load lifters behave under real weight.

06Frequently Asked Questions