All airlines become more and more keens to charge for your carry-on luggage. Especially I refer to budget airlines as they tend to check size of your bag just before entering departure gates and you don’t have any option as to pay for it as for checked bag.
Different airlines have different weight and size requirements, so if you are flying with different airlines during your trip, it can be issues with your bag.
Most confusing part is that different airlines have different requirement for luggage size. So if you flew with one airline a month ago and everything was fine it doesn’t mean your luggage measurements will comply with other company’s rules. So check these rules before you start packing as you bag may to big for your carrier.
In future posts I will try to compare requirements of different airlines, thought they tend to changes these requirements from time to time.