How to Choose a Hiking Backpack: Complete Sizing Guide

Choosing a hiking backpack comes down to three numbers: volume (liters), torso length (inches), and target load. Get those three right and almost any reputable pack will be comfortable. Get them wrong and the most expensive pack on the market will still hurt.

Step 1 — Pick the right volume

Match pack volume to your typical trip length:

• 15–25L: short day hikes, water + snacks + rain shell.
• 25–35L: full-day hikes, more layers, full 10 essentials.
• 35–50L: overnight to 3-day backpacking trips.
• 50–65L: multi-day treks or cold-weather backpacking with bulkier gear.
• 65L+: long-distance, winter, or guided trips with shared group gear.

Don’t oversize — a 65L pack used as a daypack always ends up overpacked. Run your trip through our Backpack Weight Calculator for a personal volume target.

Step 2 — Measure your torso length

Torso length matters more than your height. Measure from the C7 vertebra (the bump where your neck meets your shoulders) to a line drawn between your iliac crests (top of your hip bones). Most packs come in S, M, L sizes:

• Under 16″ → small / women’s small.
• 16–19″ → medium / men’s small.
• 19–22″ → large / men’s medium-large.

If your torso is between sizes, an adjustable suspension model lets you fine-tune fit. Adjustable-torso hiking backpacks on Amazon→

Step 3 — Match the suspension to your load

The pack’s frame and hipbelt determine how much weight it can carry comfortably:

• Frameless or minimal-frame — up to ~25 lb (ultralight setups).
• Internal frame, basic suspension — up to ~35 lb (most weekend trips).
• Full internal frame, padded hipbelt — up to ~50 lb (multi-day or winter).

If your loaded weight exceeds the pack’s carry capacity, the hipbelt collapses and the weight transfers to your shoulders — exactly what you’re trying to avoid.

Hip belt fit is non-negotiable

The hipbelt should wrap your iliac crests with the weight resting on the bony rim, not above or below it. A properly fitted hipbelt carries 70–80% of pack weight; your shoulders just stabilize.

What about ventilation?

Trampoline-style mesh suspensions keep your back cooler but push the load slightly away from your spine. Direct-contact suspensions hug your back closer (better load control) but breathe less. Pick based on climate — hot trails favor mesh; alpine trails favor close-fit.

Editor pick approach

For most hikers, a 40L pack with an adjustable torso and load-stabilizing hipbelt does 80% of jobs well. Browse 40L hiking backpacks on Amazon→. Pair it with the right loadout using our Hiking Gear Planner and run it through the Backpack Load Optimizer before you buy.

Read next

Read nextBest Hiking Backpacks Under $200: What to Look For
Read nextUltralight Backpacking Gear: Sub-15 lb Base Weight Setup

Plan it with our free tools: Pack Weight Calculator · Hiking Gear Planner