To the Millimetre

The constraint that shapes every travel bag designed for overhead use rarely appears in the marketing copy. It is not a material or a construction method or a design philosophy. It is a measurement taken by an airline employee at a boarding gate.

Why Airlines Settled on a Single Standard

The IATA standard for international carry-on luggage, adopted as a global target in 2025, sets the maximum external dimension at 56 by 36 by 23 centimetres, or 22 by 14 by 9 inches, handles and wheels included. Most major carriers in the US and Europe have aligned with it. American Airlines, Delta, and United all enforce the 22-by-14-by-9 limit. A growing number of airports now use automated sizers at boarding gates, with United having deployed them at 35 locations in late 2025 and planning to expand further.

The appeal of a unified standard is clear. Industry figures suggest that consistent carry-on enforcement could reduce boarding time by four to six minutes per flight and save over a billion dollars annually in related delays. The sizers do not negotiate. If a bag is outside the envelope, it goes in the hold.

What Designing to the Carry-On Limit Costs

Working inside a fixed external footprint is a geometry problem. The more structure you add to the outside of a bag, the less interior volume remains for the same overall dimension. External pockets reduce interior depth. A welded waterproof base panel adds a few millimetres to the profile. A structured framesheet or back panel adds to the bag's external thickness. None of these are neutral decisions when the total external measurement is fixed.

Db, the Norwegian brand known for aerospace-inspired construction and compression-structured carry luggage, made a clear choice when designing to this limit. Rather than reducing interior volume to accommodate external structure, they kept the external profile clean and routed structural decisions internally. The result is a bag that passes the sizer and uses as much of the remaining envelope as possible. Whether that trade is right depends on what you are carrying, but the trade is clearly stated in the design.

The alternative approach, designing slightly inside the limit with a small working margin, is arguably more useful in practice. Not flush to the edge, but 10 to 15 millimetres short of it, leaving room for a base that flexes under load, or a zip that adds a few millimetres of external dimension when fully loaded. A bag designed exactly at 56 centimetres in a clean showroom can measure differently when packed and handled.

How Internal Volume Gets Decided

When we are evaluating bag dimensions for the Canard carry range, the compliance limit is one of the earliest constraints we set. It governs the outer footprint before material or organisational decisions do. From there the choices compound: how much of that external dimension is taken by structure and materials, how much remains as usable interior volume, and how those volumes should be divided. A second internal packing compartment takes depth from the main body. A laptop panel borrows from the interior profile. Padding on the back panel reduces the effective interior width.

Each decision is made inside a fixed envelope. The carry-on limit is invisible in the finished product. But it is present in every dimension of it.