Rules at a glance
The table below summarises published guidance at the time of writing. Airlines revise limits, fares and fees often, and some rules depend on your ticket type, so please treat it as a starting point and confirm on the airline's own website before you fly.
| Airline | Under-seat item | Overhead cabin bag | Notes |
|---|---|---|---|
| Ryanair | 40 × 20 × 25 cm (free) | 55 × 40 × 20 cm | Larger bag with Priority & 2 Cabin Bags; 10 kg limit |
| easyJet | 45 × 36 × 20 cm (free) | Up to 56 × 45 × 25 cm | Larger bag is a paid or fare-based option; 15 kg limit |
| Wizz Air | 40 × 30 × 20 cm (free) | 55 × 40 × 23 cm | Larger trolley with priority; 10 kg limit |
| British Airways | 40 × 30 × 15 cm | 56 × 45 × 25 cm | Both items normally allowed; you must be able to lift the bag unaided |
| Lufthansa | 40 × 30 × 10 cm | 55 × 40 × 23 cm | Hand baggage up to 8 kg |
| United | 17 × 10 × 9 in (about 43 × 25 × 23 cm) | 22 × 14 × 9 in (about 56 × 36 × 23 cm) | Basic Economy fares may allow a personal item only |
| American Airlines | 18 × 14 × 8 in (about 45 × 35 × 20 cm) | 22 × 14 × 9 in (about 56 × 36 × 23 cm) | Check fare type and route |
| Delta | Must fit under the seat | 22 × 14 × 9 in (about 56 × 36 × 23 cm) | Fare type can change what is included |
You may also hear about 55 × 35 × 20 cm. That is the size IATA, the airline trade association, has suggested as a common cabin bag standard. It is a helpful guide, but it is not a rule any airline must follow.
How to measure honestly
Measure your bag the way the gate agent would: packed, standing, at its widest points, with wheels, handles, side pockets and any bulge included. Use a rigid tape measure, not a guess. Then compare each side with your airline's limit, and add a small margin so a soft bag has room to be pushed into a sizer.
- Measure height, width and depth with the bag fully packed.
- Include wheels, feet, handles and external pockets.
- Weigh the packed bag with a luggage scale and note the airline's limit.
- Leave a centimetre or two of margin on every side.
- Take a screenshot of the airline's baggage page for your trip.
Where the rules bite
Gate sizers are the classic moment of truth, but there are other hurdles. Fare type matters: a basic fare can include less than a standard one, even on the same flight. Partner and codeshare flights may follow the operating airline's rules, not the one on your booking. Small regional aircraft often have smaller bins. And a bag that is welcome at one end of a trip can be refused at the other, so check every leg.
Two non-size rules catch people too. Liquids usually have to be in containers of 100 ml or less inside one clear bag, although some airports with newer scanners are relaxing this, so check yours. Spare lithium batteries and power banks must travel in the cabin, never in a checked or gate-checked bag.
A calm way to check
Find your airline's baggage page. Note both the under-seat and the overhead allowance, and whether your fare includes the larger one. Compare the numbers with your measurements. Then, if you are within a centimetre of any limit, pick a smaller bag or accept a fee in advance, which is almost always cheaper than at the gate. For bag ideas that fit, see hard-shell cases, soft holdalls and under-seat bags.