Fly Ryanair pretty often and usually just bring the free small personal bag. It’s a soft backpack and the dimensions are technically correct.
The thing is when putting it in the bag sizer, the backpack kind of bulges out in the front because it’s soft. It still goes into the frame, but the “belly” sticks out a bit.
Never had it measured before so it hasn’t been an issue yet, but wondering if that would technically be considered too big. Feels like if the front of the sizer was closed it would probably compress and fit anyway.

