Cabin or carry-on baggage must be the correct size as it will need to be stored in the aircrafts overhead compartments or under the seat in front.
Depending on the airline and fare purchased, passengers may be able to take up to two pieces on-board. It is always best to check with your airline.
Why are the airlines so strict with cabin baggage weights?
The main reason that airlines are so strict regarding the weight of cabin baggage is safety. The overhead lockers inside an aircraft are designed only to hold a particular weight. If the aircraft experiences turbulence, the doors of the overhead lockers can be jolted open and the cabin baggage does have the potential of falling out. If this happens the person sitting below the locker could be seriously injured if the bag falling on them weighs more than 7 kgs.(15lbs)
Passengers need to expect that their cabin baggage will be weighed and measured at check in. If the bag exceeds the allowance it will need to be checked in and additional charges may apply. It is now common practice for airlines to measure and weigh all cabin baggage as well as the checked baggage.
Does it really matter if I turn up with more cabin baggage than I am permitted?
The simple answer is yes.
Apart from the safety issue, the heavier the aircraft, the more fuel that it will burn to travel to a destination. If more fuel is required due to the weight of the aircraft then it is ultimately the passengers who will end up with fare increases to cover the bill.
For further reading regarding baggage please refer to the following links: