Quick answer
A 55 x 40 x 20cm cabin case fits the limits of most major airlines, and a 40 x 30 x 20cm bag fits the free under-seat allowance on Ryanair, Wizz Air and easyJet. Always measure including the wheels. For checked luggage, choose a 24 to 26 inch case for 15kg to 20kg, or a 28 to 29 inch case for 23kg to 25kg.
Packing for a trip should feel exciting, not stressful. Yet so many of us end up at the gate, holding our breath while staff check if our bag fits the sizer. In fact, one Which? reader was charged £70 for a case that was just half a centimetre too big.
That's exactly why we put together this simple suitcase size guide. Below, we'll walk you through how to measure your bag, which suitcase size suits your trip, and the latest allowances for the airlines UK travellers use most. By the end, you'll know exactly what to pack and what to buy.
How do you measure suitcase size?
To measure suitcase size, measure the height, width and depth of your case at the widest points, including the wheels, handles and any front pockets. Airlines check the total outside size, so those extras always count.
H is floor to the top of the handle when it's pushed down, W is the widest point across the body including any pockets, D is front to back including the wheels.
Height.
Stand your case upright and measure from the bottom of the wheels to the top of the handle when it's pushed down.
Width.
Measure across the front at the widest point, including any side handles or feet.
Depth.
Measure from front to back at the deepest point, with your front pockets full.
Weight.
Weigh your case once it's fully packed, not before.
It also helps to keep a small handheld luggage scale at home. They cost very little, and one could easily save you from a nasty surprise at the check-in desk.
What size suitcase do I need?
The right suitcase size depends on your weight allowance. As a simple rule, a 20 inch case suits up to 10kg, while a 28 to 29 inch case suits 23kg to 25kg.
Cabin, medium, large and extra large cases shown in proportion, each labelled with the weight it's typically built for and what it suits.
| Suitcase size | Best for | Great for |
|---|---|---|
| Cabin or carry-on (20") | Up to 10kg | A weekend away or a short city break |
| Medium (24 to 26") | 15kg to 20kg | A 1 week holiday |
| Large (28 to 29") | 23kg to 25kg | A 2 week holiday or family packing |
| Extra large (30 to 32") | 25kg up to 32kg | Long-haul trips, visiting family abroad or moving |
Of course, these are guides rather than strict rules. Every case is built a little differently, so the design and the way you pack both play a part in how much it holds.
How to fit more into a smaller case
Choose an expandable case
An expander zip gives you extra room when you need it. For example, a 26 inch case with an expander could fit up to 25kg, depending on the case.
Go for detachable wheels
On under-seat bags and cabin cases, removable wheels free up space inside and help your bag pass the sizer.
Pick a lightweight case
The lighter your empty case, the more of your allowance goes on the things you actually need.
Wear your bulkiest items
Trainers, jumpers and coats take up loads of room, so wear them on the plane instead.
What are the cabin bag sizes for each airline?
Most budget airlines now only include a small bag that fits under the seat in front of you. There are two main sizes to know: 40 x 30 x 20cm on Ryanair and 45 x 36 x 20cm on easyJet. Other airlines usually sit somewhere in between.
If you'd like a bigger cabin case, British Airways includes a 56 x 45 x 25cm bag for free. On easyJet, you can pay to add a large cabin bag of 56 x 45 x 25cm. However, if you fly with lots of different airlines, a 55 x 40 x 20cm case is the safest choice, because it fits almost every cabin limit.
Allowances change often and depend on your fare, so always check with your airline before you fly. Correct as of September 2026.
Suitcase size FAQs
What is the standard carry-on suitcase size?
The safest carry-on size is 55 x 40 x 20cm, because it fits the cabin limits of almost every major airline. Some airlines, like British Airways and Jet2, allow a slightly bigger 56 x 45 x 25cm case.
Do suitcase measurements include wheels?
Yes. Airlines measure the total outside size of your bag, so wheels, handles and front pockets all count towards the limit.
What size suitcase do I need for 23kg?
A large 28 to 29 inch case is usually the best fit for a 23kg allowance. A 26 inch case with an expander can also work, depending on the case.
What size suitcase do I need for 1 week?
For a 1 week holiday, a medium 24 to 26 inch case is ideal. It typically holds 15kg to 20kg, which is plenty for most week-long trips.
Which airline has the biggest free under-seat bag?
Of the airlines UK travellers use most, easyJet has the biggest free under-seat bag at 45 x 36 x 20cm. Ryanair, Wizz Air and TUI allow 40 x 30 x 20cm.
Ready to find your perfect case?
Now that you know your sizes, the fun part begins. At Bag Shack, we stock everything from under-seat bags and 20 inch cabin cases to large family suitcases, so you can pack with total peace of mind.
Not sure which one is right for your trip? Pop into our Slough store or send us a message, and our friendly team will happily help you choose the perfect case for your airline, your allowance and your budget.
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