What size carry-on fits the most airlines

Start with what each airline actually publishes, sorted

Sorted largest to smallest, most US and Canadian full-service carriers publish 22 x 14 x 9 inches with wheels and handles included: American, Delta, United, Alaska, JetBlue, Hawaiian, Breeze, WestJet, Virgin Atlantic and Qantas all use that figure. Southwest and Frontier are more generous at 24 x 16 x 10 inches. Spirit publishes 22 x 18 x 10 inches, and Allegiant 22 x 16 x 10 inches. Air Canada is slightly tighter at 21.5 x 15.5 x 9 inches.

Europe's most common published figure, once converted from centimeters, works out to about 21.7 x 15.7 x 9.1 inches (55 x 40 x 23 cm), stated by Lufthansa, Swiss, Turkish Airlines and Wizz Air. Wizz Air measures that figure without wheels or handles and allows those to add up to about 2 more inches. Ryanair publishes a shorter height, 20 cm, about 7.9 inches. Air France and KLM publish a narrower width, 35 cm, about 13.8 inches. Two airlines stand apart: Qatar Airways at 20 x 15 x 10 inches has the shortest length cap in this guide's data, and Icelandair at 21.6 x 15.7 x 7.8 inches has the lowest height cap.

Do the arithmetic: what is the smallest box that clears the most airlines?

Comparing every published limit side by side, the tightest number for each dimension comes from a different airline. Qatar Airways sets the shortest length, 20 inches. Air France and KLM set the narrowest width, about 13.8 inches. Icelandair and Ryanair set the lowest height, about 7.8 to 7.9 inches. A box built to clear every single airline in this guide's data would have to be roughly 20 x 13.8 x 7.8 inches, which is smaller than almost any product sold as a full-size carry-on and would leave very little packing volume.

Stepping back from those three outliers, the next tightest bottleneck belongs to Emirates at 21.6 x 14.9 x 8.6 inches, a far more workable target that still clears the large majority of airlines in this guide.

The result: a real product at 21.46 x 13.78 x 8.66 inches

The CENSIEN 20 inch hardside (B0CZTKK4JL, $74.99) lists its size, with the wheels and handle included, at 21.46 x 13.78 x 8.66 inches. That lands just under Emirates' bottleneck on two of three sides and clears every US and Canadian limit in this guide's data with room to spare.

• Clears comfortably: American, Delta, United, Alaska, JetBlue, Hawaiian, Breeze, WestJet, Virgin Atlantic, Qantas, Southwest, Frontier, Spirit, Allegiant, Lufthansa, Swiss, Turkish Airlines, Wizz Air, easyJet, Aer Lingus
• Right at the line: Air Canada (length), Air France and KLM (width, converted from 35 cm, essentially a tie with this bag's 13.78 inch width)
• Does not clear: Qatar Airways (too long), Icelandair and Ryanair (too tall), Emirates (too tall by about a tenth of an inch)

Which specific airlines does this size not clear?

Qatar Airways' 20 inch length cap is shorter than nearly every other airline in this guide, so any bag built to the common 22 inch length will not clear it regardless of width or height. Icelandair and Ryanair both cap height at around 20 cm, about 7.8 to 7.9 inches, well under the 9 inches most full-service carriers allow. Emirates' 8.6 inch height cap is close enough that this bag misses it by roughly a tenth of an inch, which is worth double-checking with a tape measure rather than assuming either way.

Is a slightly bigger, more common size worth the tradeoff?

Most travelers fly US, Canadian or mainstream European carriers, where the 22 x 14 x 9 inch or 55 x 40 x 23 cm figures are the norm. A bag sized to that more common limit buys noticeably more packing room while still clearing the majority of airlines. Only step down to a smaller size like this one if Qatar Airways, Icelandair, Ryanair or Emirates show up regularly on the itinerary.

What about Singapore Airlines, which publishes one total instead of three numbers?

Singapore Airlines publishes only a combined length plus width plus height total of 115 cm, not separate sides. Adding this bag's own three sides together comes to about 43.9 inches, roughly 111.5 cm, which clears that total with a few centimeters to spare.