Three measurements and a weight, taken the way the sizer at the gate takes them. It takes two minutes and a tape measure.
Why a few centimetres decide it
Cabin bag limits are checked against the size the operator publishes, often with a
metal frame at the gate that your bag has to slide into. A bag that is a couple of
centimetres over can end up in the hold or on a bill, depending on the operator's
rules. Almost every time, those centimetres are wheels, a handle or a full front
pocket that nobody counted.
What you need
A tape measure. A rigid one is easier to hold straight than a sewing tape.
The bag packed the way you will travel.
A flat floor, and a bathroom scale for the weight.
Step by step
Pack it first. A soft bag or an expandable zip grows once it is
full. Measure the bag you are going to carry, not the empty one.
Push the telescopic handle all the way down and stand the bag
upright on the floor.
1 · Length (the longest side): from the floor — the bottom of the
wheels — to the highest point, which is usually the top of the carry handle.
2 · Width (the middle side): across the front, at the widest
point. Side handles, feet and corner bumpers count.
3 · Height (the shortest side, the depth): from front to back at
the widest point. Front pockets and bulges count.
Weight: stand on the scale holding the bag, then without it, and
subtract.
The mistakes that get bags stopped
Trusting the label. The size in the shop or on the tag may be the
body of the bag only, without wheels or handles.
Measuring it empty. A full bag is bigger than an empty one.
Leaving out the wheels. Spinner wheels alone can add several
centimetres to the longest side.
Forgetting the front pocket. It is part of the depth once
something is in it.
Rounding down. If the tape says 55.5 cm, the bag is 55.5 cm.
Wheels and handles: it depends on the operator
Some operators include wheels and handles in their limit. Others measure the body
of the bag and let the wheels add a set number of centimetres on top. Some don't say.
Each operator page on this site tells you which, in the operator's own terms, and the
bag checker takes it into account.
Which one is the length?
Operators usually list three figures with the longest first, but they don't all
name them the same way. On this site the order doesn't matter: the checker compares
your longest side with their longest side, and so on, because a bag can be turned —
exactly as it would be in the sizer.