Samsonite Theorym Softside Underseater: 18 x 14 x 9 in
18" underseat / personal item, softside, 4 spinner wheels, 5.1 lb empty. Exterior figures are the maker's own, wheels and handles included.
Under the seat at 0 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.
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Does the Theorym fit? All 19 airlines
18 x 14 x 9 in against each airline's published carry-on box, largest side to largest side, sorted best fit first.
| Airline | Cabin max (in) | Verdict | Under seat |
|---|---|---|---|
| Sun Country Airlines | 24 x 16 x 11 | Cabin approved2 in to spare | No |
| Allegiant Air | 22 x 16 x 10 | Cabin approved1 in to spare | No |
| British Airways | 22 x 18 x 10 | Cabin approved1 in to spare | No |
| Frontier Airlines | 24 x 16 x 10 | Cabin approved1 in to spare | No |
| Southwest Airlines | 24 x 16 x 10 | Cabin approved1 in to spare | not published |
| Qatar Airways | 19.69 x 14.57 x 9.84 | Tight squeeze0.6 in to spare | not published |
| Lufthansa | 21.65 x 15.75 x 9.06 | Tight squeeze0.1 in to spare | No |
| Turkish Airlines | 21.65 x 15.75 x 9.06 | Tight squeeze0.1 in to spare | No |
| Air Canada | 21.5 x 15.5 x 9 | Tight squeeze0 in to spare | No |
| Alaska Airlines | 22 x 14 x 9 | Tight squeeze0 in to spare | not published |
| American Airlines | 22 x 14 x 9 | Tight squeeze0 in to spare | No |
| Avelo Airlines | 22 x 14 x 9 | Tight squeeze0 in to spare | No |
| Delta Air Lines | 22 x 14 x 9 | Tight squeeze0 in to spare | not published |
| Hawaiian Airlines | 22 x 14 x 9 | Tight squeeze0 in to spare | not published |
| JetBlue Airways | 22 x 14 x 9 | Tight squeeze0 in to spare | No |
| United Airlines | 22 x 14 x 9 | Tight squeeze0 in to spare | No |
| Air France | 21.7 x 13.8 x 9.9 | Gate check0.2 in over | No |
| Emirates | 21.65 x 14.96 x 8.66 | Gate check0.3 in over | not published |
| Ryanair | 21.65 x 15.75 x 7.87 | Gate check1.1 in over | No |
Bag spec source: shop.samsonite.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.
Samsonite's own product pages list two figures per case in inches: External Dimensions (labeled by Samsonite as including the handles and wheels) and Internal Dimensions (labeled as the case without handles or wheels, i.e. packing dimensions). Both are given as H x L x W on their spec tables; this file reorders each triple to l (longest) / w (middle) / h (shortest) regardless of Samsonite's own axis labels. Live samsonite.com was bot-blocked for most of this compilation session, so many entries were extracted from web.archive.org snapshots of the same official samsonite.com product pages, as noted per entry.
All 15 Samsonite bags
