I appreciate the help on another newbie question. I really only have a lot of experience on US airline domestic flights, and really just United and Southwest/JetBlue at that. The last time I flew outside the North American range was nearly 20 years ago.

My carry on spinner, while nominally 20", is more like 23" when you count the wheels. It's also more like 9" thick. Am I going to have to check that?

It's just that from US domestic carrier experience, you want to carry on as much as possible. However, this is for vacation. I'm going to be at the airport about 3 hours early, and will already have to check a 25" bag, and going with family so my luggage/carry on allowance space is fine and will already be waiting at baggage claim. Luggage going there will be two backpacks (carry on), the 25" and the two "carry on" size rollaboards between 4 people. If I can carry it on, I'd like to stick the smaller rollaboard inside the 25" so I'll have an extra empty suitcase to bring home goodies with. Then, I'd still have my carryon with me filled with clothes and stuff in case of delays, etc. The two backpacks are going to be stuffed with electronics and things like that. Not clothes/toiletries.

If it helps, I'm going SFO-ICN on an a350 and then ICN-KIX on an a330. Not sure about the carryon space on each of those types of planes. I'd imagine the a350 has big spaces, but no idea about the a330.