How this calculator works
Airlines, couriers and some storage rules size a bag by adding its three outer dimensions, called linear inches or linear centimetres. It is not a volume and it does not care about the shape: a long thin bag and a cube with the same sum both pass the same check. Measure the outside of the bag with the pockets and wheels included. The calculator uses the engine length units, so you can enter any two sides in centimetres and the third in inches and the result is still correct. The reverse mode is the useful one when buying a bag: fix the airline limit, subtract the width and height you already have, and the remainder is the deepest the bag can be.
Formula
linear inches = length + width + height. Missing dimension = limit - the other two dimensions.
Worked example
A 55 cm by 40 cm by 20 cm bag is 55 + 40 + 20 = 115 cm, which is 45.3 linear inches. Under a 45 inch limit, a 55 cm by 40 cm bag can be at most 114.3 - 55 - 40 = 19.3 cm deep.
Advertisement
Frequently asked questions
Do airlines measure in linear inches or linear centimetres?
Each airline publishes its own limits, and some use inches while others use centimetres. The sum is the same measurement in different units, so switch the output unit to match whatever the airline states.
Do wheels and handles count?
Yes. Measure the bag as it will be checked, with the wheels, handle and any packed pockets included, because that is what the sizing frame measures.
Why is linear size not the same as volume?
Because it ignores how the space is distributed. A 20 cm by 20 cm by 100 cm tube and a 46.7 cm cube both add to 140 cm, but the cube holds far more. Volume limits catch that; linear limits do not.
Does the order of the dimensions matter?
No. Addition is commutative, so labelling the long side length or width makes no difference to the total.