Each airline has its own rules for the size and weight of checked bags. Fees for carrying baggage are also different depending on the flight operator. Before you get to the airport, you should take a minute to check if your baggage meets the size and weight rules relevant to your ticket, because additional fees for exceeding the limits tend to be rather high.
Baggage sizes include so-called snag elements – handles, wheels, etc. This is especially important for hand luggage, which usually has to fit under or over a seat in a space with specific dimensions.
The extra fee for a baggage allowance after purchasing the ticket can be higher than the fee you would pay when you are in the process of booking a ticket. Any differences result from airline policies. Make sure to choose the appropriate baggage size when making your reservation.