A4 · the sizer
Measure it before the gate does
Choose the airline, choose the slot, then copy the three numbers off the tag. Both boxes are sorted before they meet, so a bag cannot pass by being turned on its side.
How to hold the tape
Three places people measure wrong
01 · the wheels
Start at the floor
Measure from the bottom of the wheels to the top of the handle, not from the shell. Four wheels add four to five centimetres.
02 · the pockets
Fill it first
An empty side pocket measures flat. The same pocket with a bottle in it is the width the sizer sees.
03 · the depth
Depth is the one that fails
A bag packed proud is deeper at the bottom than the tag says. Overpack by two centimetres and a 23 cm frame becomes a hold bag.
Tape says it is over?
Fourteen bags on the stall have the frame count already worked out, measured the same way this page measures.