Key takeaways
- A backpack carries gear on your back, sized by capacity in liters (daypacks ~15–30L, multi-day 50L+).
- A hip belt transfers most of the weight to your hips, where you carry load far more comfortably than on your shoulders.
- Most modern packs use an internal frame; external frames suit very heavy or bulky loads.
- Fit comes first: matching the pack's torso length to your back is more important than features or brand.
How a backpack works
A backpack carries your load via shoulder straps, but a good one does most of its work through the hip belt: a frame transfers the weight down to the belt, which rests on your hip bones so your strong legs carry it rather than your shoulders. Load-lifter straps angle from the shoulders back to the frame to keep the load close and balanced.
Types by capacity
- Daypack (~15–30L) — day hikes; usually frameless or lightly framed.
- Overnight / weekend (30–50L) — one to two nights or lightweight setups.
- Multi-day (50–70L) — the standard backpacking range.
- Expedition (70L+) — winter, mountaineering, or long unsupported trips.
Frame and fit
Most packs use an internal frame that hugs the body; external frames handle heavy, boxy loads (see internal vs external frame). Whichever you pick, fit by torso length, not height.
A backpacker loading a 60L pack puts heavy items (food, water) centered and close to the back, cinches the hip belt onto the hip bones first, then snugs the shoulder straps and load lifters — so the bulk of the weight settles on the hips.
The bottom line
A backpack is the system that carries everything else, and the right one is defined first by fit and capacity, not features. Match the liters to your trips and the torso length to your back, load it so the weight rides on your hips, and a good pack disappears — letting you focus on the trail instead of your shoulders.
Frequently asked questions
What size backpack do I need?
Match capacity (in liters) to trip length and gear: roughly 15–30L for day hikes, 30–50L for overnight or fast-and-light trips, 50–70L for typical multi-day backpacking, and 70L+ for winter or expedition loads. Lighter gear lets you carry a smaller pack.
How should a backpack fit?
The key is torso length, not your height — the pack's frame must match the distance from your hips to your shoulders so the hip belt sits on your hip bones. When fitted right, 70–80% of the weight rides on your hips, not your shoulders, with load-lifter straps angling back to the frame.
Internal or external frame backpack?
Internal-frame packs hug the body for balance and are now standard for most hiking; external frames carry heavy, bulky, or boxy loads with great ventilation but ride less stably on rough terrain. See our internal vs external frame pack comparison.
Sources
- Choosing a backpack — American Hiking Society
- Pack fit & loading — The Mountaineers