The International Air Transport Association (IATA) sets guidelines for cabin baggage/hand luggage/carry-on luggage size. They are not mandatory, however, and individual airlines can and do vary their requirements. The IATA guideline states:

Cabin baggage should have maximum length of 22 in (56 cm), width of 18 in (45 cm) and depth of 10 in (25 cm). The sum of these three dimensions should not exceed 45 in (115 cm). These dimensions include wheels, handles, side pockets, etc.

As an example of the lack of standardisation some of the following airlines requirements are:

• Austrian Airlines - Hand luggage may not exceed 8 kg in weight or a maximum size of 55 cm x 40 cm x 23 cm.
• British Airways - One bag; 56 cm x 45 cm x 25 cm (22 in x 18 in x 10 in) 
• EasyJet - One bag; 55 cm x 40 cm x 20 cm 
• Jet Airways - Hand baggage dimensions vary according to the model of aircraft. 
• Malaysian Airlines - One bag; total length 115 cm (56 cm x 36 cm x 23 cm) or 45 inches (22 in x 14 in x 9 in), not exceeding 5 kg 
• Virgin Atlantic - One bag; not larger than 23 cm x 36 cm x 56 cm (9 in x 14 in x 22 in) overall and should also not weigh more than 6 kg 

Following the increase in restrictions imposed on flights from UK airports and to the USA after the events of August 2006 (2006 transatlantic aircraft plot), hand baggage on such flights was restricted to one cabin bag no bigger than 45 cm x 35 cm x 16 cm . On 21 September 2006, the UK government advised that from the following day, the allowable size of the single item of hand baggage on outgoing flights from the UK would be increased to 56 cm x 45 cm x 25 cm (ca. 22 in x 18 in x 10 in), the IATA guideline size.

Commercial airline pilots and flight attendants also comply with standards. Those standards are set by individual airlines under "uniform restrictions" which guide and maintain professional dress codes.

Source: Luggage - Wikipedia, the free encyclopedia