The right size for your carry-on and checked luggage depends on how long you'll be away from home and how much you like to pack. As a rule, 18-20 inches is ideal for international carry-on luggage. Some budget international airlines have strict size guidelines, but these bags meet those limits. If you only travel domestically, a 21 to 22-in carry-on bag is the most popular choice. For check-in suitcases, a 23- or 24-in suitcase is probably the smallest you should consider. A 25 to 27-in suitcase is the most common, especially for couples sharing. There are 28 to 32-in suitcases available if you need extra space for long trips away. However, they can be difficult to manage and too large and heavy for some airlines.