The "ideal" luggage size depends entirely on your travel habits, but for the modern traveler, a 21 or 22-inch (55cm) carry-on is generally considered the gold standard. This size is designed to fit in the overhead bins of most major domestic and international airlines, allowing you to bypass baggage claim and avoid the risk of lost luggage. A 40 to 45-liter capacity is usually enough for a 3 to 7-day trip if you pack efficiently using cubes. If you are a heavy shopper or traveling for more than two weeks, a medium-sized checked bag (around 24 to 26 inches) is a better choice, as it provides more space without becoming so heavy that it exceeds the 50lb (23kg) weight limit common on most carriers. Large 28 to 30-inch suitcases should be used with caution; while they hold a vast amount of gear, they are cumbersome to navigate through European train stations or up narrow stairs and are very easy to overpack beyond weight limits. For the ultimate versatility, a "one-bag" approach using a 35 to 40-liter travel backpack is increasingly popular, as it offers the hands-free mobility of a hiker with the organization of a traditional suitcase, making it ideal for multi-destination trips.