Carry-on Luggage Size Checker (115 cm rule)

Understanding the carry-on luggage size checker — concept and principle

Airlines limit cabin bags in two ways: by a box of maximum height, width and depth, or by the sum of the three sides. This checker adds up your bag's dimensions and tests them against several widely used limits, including the 115 cm sum common on many Asian carriers, the IATA Cabin OK guideline box of 55 × 35 × 20 cm, the US-style 22 × 14 × 9 inch box and the 158 cm sum often used for checked bags, plus a weight check against 7 and 10 kg.

How it is calculated

• Sum S = height + width + depth (cm, wheels and handles included).
• IATA 55 × 35 × 20 box: passes only if height ≤ 55, width ≤ 35 and depth ≤ 20, in the order entered.
• 115 cm rule: passes if S ≤ 115.
• US box (56 × 36 × 23 cm): the three sides are sorted from largest to smallest and each must fit its slot.
• Checked limit: passes if S ≤ 158 cm (62 in).
• Weight: ≤ 7 kg is marked as meeting the strictest common limit; ≤ 10 kg as within the other common limit.

The principle

Overhead bins and under-seat spaces are fixed boxes, so airlines either describe the box directly or use the linear sum as a simple proxy that is easy to measure at a gate sizer. A sum rule allows different shapes, while a box rule does not: a long, thin bag may pass 115 cm but fail 55 × 35 × 20. Weight limits exist because bins and the people lifting bags have limits too.

Worked example

Default: 55 × 40 × 20 cm, 7 kg.

1. Sum: 55 + 40 + 20 = 115 cm, so it is within the 115 cm limit.
2. IATA box: 55 ≤ 55 and 20 ≤ 20, but 40 > 35, so it fails 55 × 35 × 20.
3. US box: sorted sides 55, 40, 20 against 56, 36, 23; 40 > 36, so it fails.
4. 115 ≤ 158, so it passes the checked-bag limit.
5. 7 kg ≤ 7 kg: meets the strictest common limit.

How to read the result

A tick means your bag fits that particular common limit, not that your airline accepts it; here the bag passes the 115 cm sum yet is 5 cm too wide for the IATA box. Read your airline's rule for your route and fare: some count the bag size only, some add a personal item, and low-cost fares may include only an under-seat bag. A bag that sits exactly on the limit, like this example, has no margin for a bulging front pocket.

Common mistakes

• Measuring the shell only and leaving out wheels, handles and side pockets.
• Measuring an empty soft bag; packed, it can grow by several centimeters.
• Assuming a "20-inch" suitcase is 20 inches including wheels; the label often refers to the body.
• Forgetting that the weight limit can include the personal item.

FAQ

Frequently asked questions

Is a 20-inch suitcase allowed as carry-on?

Often, because most are about 55 cm tall with wheels, but check the depth and the airline's box.

Is a 24-inch suitcase carry-on?

Usually not; it typically exceeds 115 cm in total and must be checked.

Does the 115 cm limit include the handle?

Generally yes: airlines measure the outside dimensions, including wheels and handles.

Sources: Airline conditions of carriage and baggage policies (check your carrier)