Peak Design Travel Backpack 20L: 18 x 11.8 x 5.7 in
20L, backpack, no wheels, 2.5 lb empty. Exterior figures are the maker's own.
Under the seat at 3 of 13 airlines with a published limit
The table below shows the verdict at every airline, best fit first, using the same math as the live fit checker.
As an Amazon Associate we earn from qualifying purchases. Links are affiliate links; it costs you nothing extra.
Does the Travel Backpack fit? All 19 airlines
18 x 11.8 x 5.7 in against each airline's published carry-on box, largest side to largest side, sorted best fit first.
Expansion warning: zipped open, this bag runs 8.4 in deep (18 x 11.8 x 8.4 in) and clears 18 of 19 airlines instead of 19. Expanded, it flips to gate check on Ryanair. Fly with it zipped shut.
| Airline | Cabin max (in) | Verdict | Under seat |
|---|---|---|---|
| Frontier Airlines | 24 x 16 x 10 | Cabin approved4.2 in to spare | Yes |
| Southwest Airlines | 24 x 16 x 10 | Cabin approved4.2 in to spare | not published |
| Sun Country Airlines | 24 x 16 x 11 | Cabin approved4.2 in to spare | No |
| Allegiant Air | 22 x 16 x 10 | Cabin approved4 in to spare | Yes |
| British Airways | 22 x 18 x 10 | Cabin approved4 in to spare | No |
| Lufthansa | 21.65 x 15.75 x 9.06 | Cabin approved3.4 in to spare | No |
| Turkish Airlines | 21.65 x 15.75 x 9.06 | Cabin approved3.4 in to spare | No |
| Air Canada | 21.5 x 15.5 x 9 | Cabin approved3.3 in to spare | No |
| Emirates | 21.65 x 14.96 x 8.66 | Cabin approved3 in to spare | not published |
| Alaska Airlines | 22 x 14 x 9 | Cabin approved2.2 in to spare | not published |
| American Airlines | 22 x 14 x 9 | Cabin approved2.2 in to spare | Yes |
| Avelo Airlines | 22 x 14 x 9 | Cabin approved2.2 in to spare | No |
| Delta Air Lines | 22 x 14 x 9 | Cabin approved2.2 in to spare | not published |
| Hawaiian Airlines | 22 x 14 x 9 | Cabin approved2.2 in to spare | not published |
| JetBlue Airways | 22 x 14 x 9 | Cabin approved2.2 in to spare | No |
| Ryanair | 21.65 x 15.75 x 7.87 | Cabin approved2.2 in to spare | No |
| United Airlines | 22 x 14 x 9 | Cabin approved2.2 in to spare | No |
| Air France | 21.7 x 13.8 x 9.9 | Cabin approved2 in to spare | No |
| Qatar Airways | 19.69 x 14.57 x 9.84 | Cabin approved1.7 in to spare | not published |
Bag spec source: peakdesign.com · accessed 2026-07-09. Airline limits come from each carrier's official baggage page; open an airline above for its citations. Policies change, so verify a borderline case before you fly.
Peak Design lists a separate exterior (external) and interior dimension set for each bag, given in centimeters with the inch equivalent in parentheses. The Travel Backpack sizes are expandable, so the page gives a standard unexpanded exterior and an expanded exterior; the exterior field here stores the standard unexpanded size and expandedDepthIn stores the expanded depth. Travel Duffels do not expand, and none of these bags have wheels or a rigid frame, so the published exterior is the soft bag body.
All 8 Peak Design bags
