Ryanair publish two different sizes for the free small bag, and both are on their own website. That is why you are here, and it is why so many people arrive at this question certain they have read one of them.
The current figure is 40 x 30 x 20 cm. It is on Ryanair's Bag Policy page, which we read on 14 September 2026 and reread every month. The older 40 x 20 x 25 appears in help articles and on some fare-bundle pages that have not been updated.
If you already own a 40 x 20 x 25 bag, it still fits
This is the useful part, and it is good news.
A gate sizer is a box. A bag does not have to go in the way you are holding it, it has to go in. So the comparison is not 40 against 40, 20 against 30 and 25 against 20. It is the three measurements of your bag against the three of the frame, largest to largest.
Sort them and you get 40, 25, 20 for the old spec against 40, 30, 20 for the current one. Every number on the left is equal to or smaller than the one on its right. A bag built to the old 40 x 20 x 25 goes into a current Ryanair sizer, turned on its side.
What you are losing is space rather than entry. The old shape holds about 20 litres. The current allowance is about 24. Buying to the outdated number costs you roughly 20 per cent of the bag you are entitled to bring.
It does not work the other way round
Run the same comparison backwards. A current 40 x 30 x 20 bag sorts to 40, 30, 20. An old 40 x 20 x 25 frame sorts to 40, 25, 20. Thirty is more than twenty five, so it does not go in, whichever way you turn it.
That matters if you are flying from an airport where the sizers have not been changed. A bag bought to Ryanair's current published allowance would fail an old frame by five centimetres. There is not much you can do about that beyond knowing it is possible.
Which number wins if a gate agent disagrees
Theirs. Always theirs.
We publish what Ryanair publish, date it, and link to their page so you can check it yourself. If Ryanair change the figure tomorrow, our page is wrong until we reread it, and the person at the gate is working from the current rule rather than from us.
Print or screenshot the Bag Policy page before you fly if you want something to point at. The page linked from our Ryanair under-seat bag size guide is the one that governs.
Why two numbers exist at all
Ryanair changed the allowance and did not update every page that mentions it. Large sites accumulate this kind of thing. The figure also circulates on third-party listings, forums and retailer product titles, all of which were written at different times, so the old number keeps being copied forward long after the source moved on.
It is worth knowing that no airline operates an approval scheme for luggage. A bag described as Ryanair approved has not been approved by Ryanair. It either measures inside the published allowance or it does not.
What to do about it
Buy to 40 x 30 x 20. It is Ryanair's current number, and it is also what Jet2, TUI and Wizz Air set, so one bag covers four carriers. easyJet allow more at 45 x 36 x 20, so you are inside theirs as well.
If you already own a bag at the old size, keep it. It fits. You are just carrying less than you have paid for.
Either way, measure it the way the gate does before you go, because the number on the label and the size of the packed bag are not always the same thing.