Backpack size is measured in liters of volume, and the right number depends on two things: how many days you are out, and how bulky the rest of your gear is. The packs we track run from 30 to 75 liters. Here is how to land on the right size without carrying dead space or leaving gear behind.
Use trip length as the starting point, then adjust for your gear:
| Trip | Typical volume |
|---|---|
| Overnight / ultralight | 30 to 45 L |
| Weekend (2 to 3 nights) | 45 to 55 L |
| Multi-day (3 to 5 nights) | 55 to 65 L |
| Extended / winter / bulky loads | 65 L and up |
These bands overlap on purpose, because the second factor moves you within them.
Two backpackers out for the same three nights can need very different packs. A compressible down quilt, a small ultralight shelter, and an air pad pack into a fraction of the space that a synthetic bag, a heavier tent, and a foam pad take up. Size the pack to your kit, not just the calendar. If your sleep system and shelter are light and compressible, size down a band; if they are bulky or you carry a bear canister, size up.
Volume is not the only number. A frameless ultralight pack (the lightest we track is well under a pound) carries beautifully up to a point, then gets uncomfortable, while a framed pack (up toward 5 to 7 lb) hauls heavy, bulky loads in comfort. Match the pack's rated load to how much your gear plus food and water will actually weigh: a big volume you overload past the frame's comfort limit is a miserable pack.
A pack's comfort depends more on torso length than on your height, and most makers publish a torso range per size (and sometimes adjustable suspension). A well-fitted 50 L pack carries better than an ill-fitting 65 L one. Measure your torso, check it against the size chart, and prioritize a pack whose range centers on your measurement.
For two to three nights, most backpackers land in the 45 to 55 L range. Size down toward 45 L if your sleep system and shelter are light and compressible, up toward 55 L if they are bulky or you carry a bear canister.
Yes. Extra volume adds weight and tempts you to fill it, and an underfilled large pack carries less stably. Size to the gear you actually carry rather than buying the biggest pack for flexibility.
Most thru-hikers run 40 to 55 L, because their kit is dialed and light. Bulky or heavier setups, or long food carries between resupplies, push toward the higher end.
Framed packs run roughly 3 to 5 lb and carry heavy loads comfortably; ultralight frameless packs can be under a pound but have lower comfortable load limits. Match the rated load to your total carried weight.
This guide explains published standards and industry specs, illustrated with figures drawn from the 500-plus products in our database. It is educational reference, not a substitute for matching gear to your own conditions. We take no sponsorships and run no paid placements.