If it looks oversized you may be asked to place your bag in the bag sizer. If it doesn’t fit you’ll need a plan B. Up to you if you’re willing to chance it.

whilst the bag may be fine on some other airlines there is no standard across airlines. I have 2 cabin bags - a smaller one that is used for Ryanair and other airlines with dimensions lower than the larger one. It sounds like your bag would not fit in the sizer gauge so you would likely be charged to place it in the hold...check out the fee, possibly be cheaper to purchase a bag that complies or borrow off a friend. If you really need more than 10kgs then purchasing hold baggage is probably the best bet.

Ryanair tend to enforce their rules.

If you want to gamble, be preoared to pay for it to be checked

You might just get away with the extra inch on the depth – I've seen that happen at MAN where they are really strict – but yes they did have scales at the gate.

I have never agreed with the way manufacturers and retailers describe bags as 'standard cabin bag size' because there is no such thing. Yes, some sizes may be more common than others across the globe, but not enough to say there is a standard in my opinion.

With Ryanair it's the sizer that matters. If you can squash the bag in you will be fine. If you can't then you will have to pay for the bage to be checked. Ryanair are strict in enforcing their rules, but I dare say they do not ask everyone to put their luggage into the sizer. It will only be if the bag looks too big. Just remember that the maximum dimesnsions include wheels and handles.

I just pay for a check in bag on Ryanair because my international flight sized carry on is too big. Be aware that their personal item size is also very small and they have sizers for those too. I've never been asked to put mine in, but I'm always well under the sizes since I check my roller bag.

ETA: I believe the baggage fees are cheapest when you buy, then more if you add online after purchase, and most expenisve if you wait until the airport. All the fees are listed on their website.

As others have said, Ryanair have a well founded reputation for rigidly enforcing their rules, and their gate staff are very good at spotting oversize bags - the sizer referred to also includes a set of scales, so if it's over 10kg, they'll find that out too.

I never take a bag that I know is over the permitted dimensions on any airline. The odds against getting away with a slightly oversize or overweight bag are higher with Ryanair because it's part of their business model to be strict.

And, in fairness, there's no point in having rules if you aren't going to enforce them properly.

If you do risk it, take a smaller squishy bag to transfer essential items as carry on - things you can't be without on a flight if your bag is refused.