Interactive tool
Backpack Volume Sizer
Get a defensible pack-liter recommendation from trip length, season, shelter style, and whether you're required to carry a bear canister — with the formula published so you can verify or cite it.
Bracket range: 41–51 L. Most packs in this range from Osprey, Gregory, Hyperlite, Granite Gear, and Zpacks will fit this kit comfortably.
The formula
liters = 30 + trip_length_bonus + season_offset + shelter_offset + ultralight_offset + bear_canister_offset
- Trip length: +8L per day for days 2–7, +5L per day for 8–12, +3L per day beyond.
- Season: summer −5L · three-season 0 · shoulder +10L · winter +22L.
- Shelter: tarp −5L · tent 0 · 4-season tent +6L.
- Ultralight kit: −15L. Bear canister: +8L. Floor: 18L.
Sources
- REI Co-op Expert Advice: How to Choose a Backpack.
- Osprey Packs sizing guide (published pack liter ranges by trip type).
- Backpacking Light gear surveys, 2019–2024 base weight vs. pack volume regression.
Last reviewed: 2026-07-25.
Frequently asked questions
Why start with liters instead of a pack model?+
Volume is the constraint that actually limits what you can carry. Pack manufacturers publish liters, not weight capacity, because a 60L pack fits roughly the same gear whether it's a Osprey Aether or a Hyperlite Southwest.
How does season change the number?+
Winter and shoulder-season kits add insulation (bulky puffy, warmer bag, thicker pad) and often a 4-season tent. Wild10 adds 10L for shoulder season and 20L for full winter on top of the base three-season recommendation.
What if I'm ultralight?+
Toggle the 'Ultralight kit' switch and the tool trims 15L off the recommendation — a UL sleep quilt, frameless pack, and tarp shelter compress dramatically compared to traditional gear.
Can I cite this?+
Yes. Link to https://wild10.com/tools/pack-volume-sizer. The formula is published on the page.