Line up to board a plane, and you will see a wide array of carry-on bags in a variety of shapes, colors and, unfortunately for the airline staff, many different sizes. While some of those oversized bags immediately get the boot, the assortment of sizes can still make it tough to maximize overhead bin space. That struggle could be a thing of the past, if carriers sign on with the industry’s new specifications for the “perfect” carry-on.

The perfectly-proportioned rolling suitcase is small enough to allow all passengers on a flight of 120 people or more to fit one bag in the overhead space near their seat, said Tom Windmuller, the International Air Transport Association (IATA) senior vice president for airport, passenger, cargo and security.

Working with Boeing and Airbus, the IATA came up with exact measurements for the ideal size: 55 centimeters (21 inches) tall, 35 centimeters (13.5 inches) wide and 20 centimeters (7.5 inches) deep. That’s a few inches smaller than the maximum many airlines set for carry-on luggage.

Because airlines set their own size requirements for carry-ons, this can lead to confusion, said Windmuller, calling sizing bins placed near the gate “ridiculous” when addressing reports, says the Associated Press.

Many airlines have different size requirements for carry-ons, which can lead to confusion, he adds.

“The development of an agreed optimal cabin bag size will bring common sense and order to the problem of differing sizes for carry-on bags,” Windmuller says in a press release (warning: link has video that autoplays). “We know the current situation can be frustrating for passengers. This work will help to iron out inconsistencies and lead to an improved passenger experience.”

The IATA worked with baggage manufacturers to make bags widely available by the end of the year. Price will vary depending on the quality and materials chosen by bag makers. If the bags fit IATA size specifications, they’ll get a label reading “IATA Cabin OK.”

To be clear — other carry-on bags will still be allowed, even without such a tag.

Airlines don’t have to sign up to be a part of the initiative, but Windmuller says airline executives have been responding well so far, with “a number of major international airlines” planning to introduce guidelines soon into their operations.

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