When it comes to shapes and sizes of bags, which ones can be carried on the airplane and what you need to know to keep airline baggage costs at a minimum is easily figured out using information from the airline carrier and elementary arithmetic. The rules are always changing for the number of bags, their size and weight and depend on your fare, destination, frequent flyer status and date of travel, so it’s a good idea to check with the airlines before you go. Keeping up with the regulations can save money and hassles at the airport. We've seen travelers struggle to offload items from their luggage into already overloaded carry-ons to avoid overweight baggage fees or run at the last minute to buy the cheapest suitcase they can find at duty free. The airline industry invented the idea of linear inches to establish their limits regarding checked and carry-on baggage allowances. The calculation is easy; just add the total of the length plus the width plus the height of the case to calculate its size in linear inches. You must include wheels and handles in your measurements. If you want to convert to centimeters, multiply the number in inches by 2.54. A typical checked bag for most North American travel in 2013 must not exceed 62 linear inches (157 centimetres) in order to avoid extra baggage fees for oversized luggage. A carry-on bag has limits of 45 linear inches (114 centimetres).