Cabin means overhead locker

A cabin suitcase is one sized for the overhead locker rather than the footwell. On low-cost carriers this is usually the paid allowance — Priority on Ryanair, WIZZ Priority on Wizz Air, the large cabin bag on easyJet. On British Airways, Jet2 and TUI it is included free.

The three cabin sizes that matter

• 55 × 40 × 20cm — Ryanair Priority. The tightest of the locker allowances, and the safest to buy for if Ryanair is in your rotation.
• 55 × 40 × 23cm — WIZZ Priority. Three centimetres deeper, which sounds trivial but means a Wizz-sized case can fail a Ryanair sizer.
• 56 × 45 × 25cm — British Airways, Jet2 and easyJet’s large cabin bag. The most generous, and what a full-size hard-shell cabin case is built for.

Buy for the tightest airline you fly

This is the single most useful rule. A 55 × 40 × 20cm case fits every allowance above. A 56 × 45 × 25cm case fits only the most generous. If you fly Ryanair even occasionally, the smaller footprint is worth the lost litres.

Weight is the hidden limit

Most cabin allowances cap at 10kg including the case. British Airways is the exception at 23kg. A hard-shell cabin case weighs roughly 2.5 to 3.1kg empty, so on a 10kg limit you have around 7kg for contents — enough for a week, but worth weighing before you leave.

Capacity, not height

Two cases both described as “cabin” can differ by 10 litres or more depending on their depth and how much the wheel housing intrudes. Compare litres rather than the figure on the label.