Sukat
The tape goes across the wheels and the handles
An airline sizer is a metal box with an opening. A bag passes if the whole bag, wheels included, goes into the opening with the sides turned any way round. Everything below follows from that one fact.
Fill it first
Soft bags bulge at the seams. Measure the bag packed the way it will board, not flattened on the floor.
Three sides only
Length, width, depth. The diagonal is not a side and no carrier publishes a diagonal limit.
Include what sticks out
Wheels, the top grip, the side pocket when full. A 55 cm shell plus wheels is often 58 cm in the sizer.
Weigh it packed
A hook scale on the handle. The cabin limit counts both pieces together on most carriers.
The checker
Try your bag against any carrier on the board
The comparison sorts the three sides of the bag and the three sides of the frame, so a bag is never failed for being turned the wrong way. It fails only when one side is genuinely longer than the matching side of the frame.
The check runs in this tab. Nothing is uploaded and the numbers are not stored.
Type the three sides and the weight, then press check. The answer prints here like a tag.
The four frames that catch most bags
Most cabin bags are sold in one of four envelopes. Knowing which envelope an airline draws explains the failures before you measure anything.
- 56 × 36 × 23 cm. Cebu Pacific, Cebgo, Philippine Airlines, AirAsia Philippines, Jetstar Asia, Singapore Airlines, Cathay Pacific, Malaysia Airlines, Vietnam Airlines and VietJet all use this one. The narrow side is 36 cm, which is where a 40 cm-wide European bag fails.
- 55 × 40 × 20 cm. Turkish Airlines, Korean Air and most European carriers. Wider and shallower: a 23 cm-deep bag fails here while a 40 cm-wide bag passes.
- 55 × 38 × 22 cm. Emirates. A centimetre narrower than the 56 cm group and a centimetre deeper than the Korean Air frame.
- 50 × 37 × 25 cm. Qatar Airways. The shortest length on the board, so a standard 55 cm trolley fails outright.
Where the weights surprise people
Seven kilos is a laptop, a charger, a folder and two days of clothes. Moving to ten kilos on Cebu Pacific's 5J flights did not change the frame, only the scale, so a bag that fits the box can still fail the hook.
On carriers that publish a shared allowance, the personal item counts in the same kilos. A 1.8 kg laptop bag leaves 5.2 kg for the cabin bag on a 7 kg allowance, which is the number the gate agent reads off the scale.