Three numbers cover almost every trip you will take.
55 x 40 x 20 cm is the cabin bag size that clears nearly every airline flying from the UK. 23 kg is the standard weight allowance for a checked suitcase. An under-seat bag is around 40 x 30 x 20 cm, and on most low-cost fares it is the only bag included in the price.
Everything else is detail. The detail is where people get caught out, so here it is.
The Three Sizes
| Bag type | Typical UK limit | In inches | Weight |
|---|---|---|---|
| Under-seat bag | 40 x 30 x 20 cm | 16 x 12 x 8 in | Rarely weighed, but must fit the sizer |
| Cabin bag | 55 x 40 x 20 cm | 21.7 x 15.7 x 7.9 in | 10 kg on low-cost carriers, and often weighed |
| Checked bag | Generous on size (BA allows 90 x 75 x 43 cm) | 35 x 29.5 x 17 in | 23 kg |
Under-seat bag limits vary more than the other two, because each airline sets its own size and enforces it with a sizer at the gate.
What Kind of Traveller Are You?
There are six types of travellers; here's what each one actually needs.
The Weekender
One or two nights. A city reset, a wellness weekend, somewhere you can reach by train before dinner. An under-seat bag does more than people expect at this length, and a small cabin bag covers it with room to spare. The trip is short enough that the bag should never slow you down.
The City Traveler
Two to four days in a place you came for the food, the galleries, or the shopping. A cabin bag, and one you are happy to be photographed with, because it is going to be beside you at a hotel desk and in the back of a taxi more than it is going to be in a hold. Leave room for what you bring home. If the flight is low-cost, the cabin bag is probably an add-on, so book it with the fare rather than at the airport.
The Cabin Bag Loyalist
You have not checked a bag in years and you are not starting now. You want the largest cabin bag that is still allowed, which means the measurement matters more to you than to anyone else on this list. Measure with the wheels and the handle included. That is how the gate measures. Then weigh it, because on low-cost carriers a cabin bag over 10 kg goes in the hold.
The Family Organiser
You are packing for more than yourself, and probably for people who packed badly. One large checked suitcase plus a cabin bag each is the usual shape. Two sizes that nest inside each other are worth more here than anywhere else, because between trips they live in a wardrobe, not an airport.
The Long-Haul Traveller
Two weeks or more, often several cities, often several climates. A large checked suitcase within 23 kg, plus a cabin bag for the things you would rather not lose. Weigh it at home. A large suitcase reaches 23 kg well before it is full. Check the cabin bag allowance too: Emirates, Qatar Airways and Singapore Airlines cap it at 7 kg.
The Buy-Once Traveller
You research, you buy properly, and you keep it for a decade. The mistake here is buying for the biggest trip you might take rather than the trip you take most. Buy for the second one, and add a size later if the first ever arrives.
How to Measure Your Luggage
Whichever of those you are, three things decide whether a bag passes.
Every dimension includes wheels, handles, and exterior pockets. A suitcase sold by the size of its shell is often a couple of centimetres taller with its wheels. This is the single most common reason a bag gets stopped at the gate.
Total dimensions means addition, not multiplication. Some airlines give one figure rather than three: Singapore Airlines allows 115 cm in total for a cabin bag. A suitcase measuring 75 x 50 x 30 cm is 155 cm in total. Volume never enters into it.
The margin is closing. More airlines now check bags against sizers at the gate rather than trusting passengers, and low-cost carriers charge for an oversized bag on the spot.
The 24-Inch Question
A suitcase sold as "24 inch" is not measured the way an airline measures. That number is the height of the bag, around 61 cm, usually including the wheels, and it says nothing about the other two dimensions.
So, plainly: a 24-inch suitcase is a checked bag. At 61 cm it is too tall for the cabin on every airline flying from the UK. A 28-inch suitcase, around 71 cm, sits comfortably inside checked size limits. The risk with a bag that size is weight, because it holds far more than 23 kg.
Where Airlines Differ
British Airways and Jet2 are the most generous. British Airways includes a 56 x 45 x 25 cm cabin bag plus a handbag or laptop bag, up to 23 kg each. Jet2 includes a 56 x 45 x 25 cm, 10 kg cabin bag plus a 40 x 30 x 15 cm personal item.
The other low-cost carriers include an under-seat bag and charge for the overhead locker. Ryanair includes 40 x 30 x 20 cm and charges for a 55 x 40 x 20 cm, 10 kg cabin bag. Wizz Air works the same way, with 55 x 40 x 23 cm on Priority. easyJet includes 45 x 36 x 20 cm, up to 15 kg, and charges for a 56 x 45 x 25 cm large cabin bag.
Checked bags are more uniform: 23 kg on British Airways and most flag carriers. Low-cost airlines sell hold luggage by weight, so the allowance is whatever you booked, and anything over is charged at the airport. Most airlines will not accept a single bag over 32 kg.
Long-haul, the cabin bag is where it varies. Emirates, Qatar Airways and Singapore Airlines cap it at 7 kg. Flying to the US, the American carriers use 56 x 36 x 23 cm and rarely weigh it.
From 2027, new EU rules are set to guarantee a free personal item of 40 x 30 x 15 cm on flights within the EU.
For exact dimensions, packing volumes, and weights across the Aviator Collection, see the Size Guide.
