Liter capacity is the standard way backpacks are sized, but translating a number into 'will my gear actually fit' takes a bit of context.
- 1
What a liter measures
A liter of pack volume is a measure of internal space, roughly equivalent to a liter of water's volume — manufacturers calculate it by measuring the total usable interior and external pocket space of the pack.
- 2
Matching liters to trip length
10-20L suits short day hikes. 20-35L suits full-day hikes or ultralight overnight trips. 35-50L suits standard 2-4 day backpacking trips. 50-70L+ suits week-long trips or winter camping with bulkier gear.
- 3
Why two packs of the same liter rating can feel different
Internal frame design, pocket configuration, and compression capability all affect how efficiently a given liter capacity is actually usable — raw volume numbers don't capture organizational efficiency.
- 4
Accounting for external attachment
Some manufacturers include external attachment capacity (for a sleeping pad or tent strapped outside) in marketed liter figures, while others measure only enclosed volume — check specifics if comparing packs closely.
- 5
When to size up versus down
Ultralight packers with minimal gear can often use a smaller liter capacity than the 'standard' recommendation for their trip length; hikers with bulkier gear or lower packing efficiency should consider sizing up.
Liter Capacity by Trip Type
| Use Case | Recommendation | Price |
|---|---|---|
| Short day hike | 10-20 liters | |
| Full day hike / ultralight overnight | 20-35 liters | |
| Standard 2-4 day backpacking | 35-50 liters | |
| Week-long or winter trips | 50-70+ liters | |