Bag Basics
Bag Volume 101: Why 1L ≠ 1L
Two bags rated 20L. One fits twice as much. Here's why.
“Think two 20-liter bags hold the same amount? Think again. Volume ratings are more misleading than most buyers realize — and what really matters when choosing a bag isn't the number on the tag.”
What is it
Volume is typically measured by filling a bag's compartments with small pellets or water and measuring displacement. But brands differ wildly in how they count: some include every exterior pocket and expansion zone, others measure only the main compartment. This creates massive real-world differences between bags with identical liter ratings. Key terms to know: usable volume (what you can actually pack), packable volume (how it compresses when empty), and perceived capacity (how efficiently the interior is laid out).
Why it matters
Real-world packing experience often doesn't match the listed volume. A 30L camera bag with heavy internal padding may carry far less than a sleek 25L commuter pack. Misleading ratings lead to overpacking, missed airline limits, or frustration when your gear doesn't fit. This gap is especially significant for travel and everyday carry, where dimensional constraints are strict.
How to identify it
Look beyond the number and consider shape and layout — a tall, narrow bag and a squat, wide bag rated at the same liters will carry very differently. Check for tapered walls, rigid vs. flexible structure, and padded dividers that eat into usable space. Test actual capacity by using packing cubes or consistent reference items (hoodie, laptop, water bottle). Also look for compression and expansion features that can meaningfully change usable space.
When you don't need it
If your use case is fixed and minimal — say, a gym bag that always carries the same few items — you don't need to stress over nuanced volume differences. Similarly, if comfort, style, or carry method matter more to you than raw capacity, the liter number becomes less critical.
What they say vs. what it means
“Think two 20-liter bags hold the same amount? Think again. Volume ratings are more misleading than most buyers realize — and what really matters when choosing a bag isn't the number on the tag.”
Volume is typically measured by filling a bag's compartments with small pellets or water and measuring displacement. But brands differ wildly in how they count: some include every exterior pocket and expansion zone, others measure only the main compartment. This creates massive real-world differences between bags with identical liter ratings. Key terms to know: usable volume (what you can actually pack), packable volume (how it compresses when empty), and perceived capacity (how efficiently the interior is laid out).
Key takeaways
- Don't take volume ratings at face value — two bags with the same liter rating can carry very different amounts.
- Shape, compartment layout, and internal structure matter more than the number.
- Always cross-reference dimensions and layout with your actual packing needs.
- Use reference items (not just the spec sheet) to test real carry capacity before buying.
Quick poll
“When shopping for a bag, how do you gauge if it's big enough?”
Want to see how this applies to your specific carry? Take the bag finder quiz →
More from Bag Basics