Capacity should match trip length and gear volume, not body size, so the liter range you need runs from about 15–25 L for a day of rock climbing up to 50–70 L for a multi-day expedition.
Buying a pack by height sends climbers back to the store twice. A 5’10” person and a 6’2″ person can wear the same torso size, and a 20 L alpine pack carries the same load on either frame. Sizing starts with two numbers: how long you’ll be out, and how much gear you’re hauling.
Torso Length Beats Height For Fit
Torso length decides whether a pack sits on your hips or rides on your shoulders. Measure from the C7 vertebra — the bump at the base of your neck when you tilt your head forward — straight down to the iliac crest line at the top of your hip bones. That number maps to the pack’s size range, not your height. A pack that sits too high or too low transfers load to the shoulders instead of the hips, the fastest way to hate a long approach.
Pack volumes include storage pockets, not just the main compartment, which is why a 35 L crag pack may hold less than a 35 L hiking pack.
Match Liters To Trip Length And Gear
Lay out your actual load — shelter, sleep system, cook kit, clothing, and food — then pick the volume that holds it with roughly 10% spare capacity. That gear-first method beats any chart, because a sport rack and a rock rack have wildly different footprints.
| Activity | Typical Capacity | What It Carries |
|---|---|---|
| Small multi-pitch rock | 15–25 L | Rack, rope on external strap, light layer, water |
| Following or seconding | 16–30 L | Personal gear, minimal rack, no lead weight |
| Versatile alpine | 30–50 L | Layers, small rack, crampons, day food |
| Cragging | 40–50 L | Full rack, rope inside, shoes, chalk, layers |
| Multi-day expedition | 50–70+ L | Tent, sleep system, cook kit, several days of food |
| 1–2 night backpacking | 20–50 L | Sleeping bag, pad, tent, stove, food |
| 2–5 night backpacking | 60–80 L | Larger shelter, more food, spare layers |
Smaller packs often lean on external rope carry — a rope strap or two over the top — so a 20 L pack can still haul a 70 m line. Once you’re carrying a full rack, a rope, and a jacket, the pack grows into the 40–50 L cragging zone, where more gear space usually wins over weight savings. If you’re comparing what’s on the market, this tested climbing backpack roundup breaks down how different models handle these loads.
Mistakes That Cost You Comfort
Picking volume by height instead of torso length is the classic sizing error and the one most pack returns trace back to. Overpacking a climbing pack hurts carry comfort and balance on alpine routes, where an off-balance load costs more than a heavy one. If you’re unsure between two volumes, take the smaller option and let a rope or helmet ride outside. The OutdoorGearLab buying advice makes the same point — the “right” liter size varies by activity, and no single number covers both a sport crag and a three-day alpine push.
A lightweight climbing backpack with the wrong torso size will still ride badly, so fit and volume are separate decisions. Get torso length first, then size liters to the gear you’re hauling.
FAQs
Is torso length really more important than my height?
Yes. Pack sizing systems use torso length because it determines where the hip belt and shoulder straps sit. A tall climber with a short torso may fit a size small, and a shorter climber with a long torso may need a large. Measure C7 to the iliac crest, then match that number to the pack’s published range.
Can I use one pack for both cragging and alpine trips?
A 30–50 L pack covers versatile alpine use, but it’s a compromise for both extremes. Dedicated crag packs at 40–50 L carry a full rack and rope inside, while smaller alpine packs stay lighter for fast objectives. If you climb both regularly, two packs sized to each trip type usually work better.
How do I know if my loaded pack is too big?
If the load shifts, the pack sags below your hip belt, or you’re cinching straps hard to stop movement, the volume is too large.
References & Sources
- Millet. “How Do You Choose a Bag for Mountaineering?” Source for mountaineering pack volume ranges by trip length.
- REI. “How to Find the Right Backpack” Source for general backpack capacity guidance by nights out.
- OutdoorGearLab. “Mountaineering Backpack Buying Advice” Source for climbing pack capacity varying by activity.