An initiative is set to see smaller bags on flights, after the air transport governing body set new targets at its annual conference.

The International Air Transport Association (IATA) wants to end the squabble of differing carry-on bag sizes and airline policies with carriers.

Working with airline members of IATA and aircraft manufacturers, it has set an optimum size guideline for carry-on bags that it says will make "the best use of cabin storage space."

A size of 55 x 35 x 20 cm (or 21.5 x 13.5 x 7.5 inches) means that, theoretically, everyone should have a chance to store their carry-on bags on board aircraft of 120 seats or larger.

But this is smaller than what is currently allowed on both Aer Lingus and Ryanair flights.

Aer Lingus lists its dimensions as 55cm x 40cm x 24cm, and Ryanair currently allows 55cm x 40cm x 20cm.

The new IATA approved bag | Image: IATA

An 'IATA Cabin OK' logo will also signify to airline staff that a bag meets the agreed size guidelines.

The IATA says a number of major international airlines "have signaled their interest to join the initiative and will soon be introducing the guidelines into their operations."

"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. 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," said Tom Windmuller, IATA's senior vice president for airport, passenger, cargo and security.

Several major baggage manufacturers have developed products in line with the guidelines, and it is expected bags carrying the IATA label will start to reach retail shops later this year.