On domestic flights within the United States, a carry-on bag that's smaller than 22 x 14 x 9 inches (45 linear inches), including handles and wheels will meet the size restrictions of all major airlines, such as United Airlines and Alaska Airlines.

To determine if your suitcase is carry-on size, you should check its dimensions against the specific requirements of the airline you are flying. The most common standard for major domestic airlines (like American, Delta, and United) is 22 x 14 x 9 inches (56 x 36 x 23 cm), including wheels and handles. For international or budget carriers, the limits are often stricter, sometimes as small as 21.5 x 13.5 x 7.5 inches. To measure your bag at home, use a tape measure for the height, width, and depth at the widest points. Many travelers also use the "sizer" bins found near airport check-in counters; if the bag fits completely within the metal frame, it is cleared for the cabin. It is also important to check the weight, as many international airlines impose a limit of 15 to 22 pounds (7–10 kg). If your bag is soft-sided, ensure it is not "overstuffed," as a bulging bag may exceed the depth limit. If you frequently fly different airlines, choosing a bag marketed as "International Carry-On" is a safer bet, as it is designed to meet the most stringent global size standards.