Carry On Luggage Within Italy

Every airline has their own rules, there is no general answer to your question.

Not every airline is necessarily going to have the same size restrictions. You need to check the requirements for the airline(s) you plan to use.

How closely the bags will be scrutinized will depend on which airline it is and what the situation is at the gate when you go to board.

If you are over any of the limits there is always the chance to be forced to check it ( and probably pay a premium price to do so)

As previously noted, it depends on which airline you are using. Having said that, it also depends on the gate agents. On a flight from Florence to Rome on our way to JFK Alitalia made us check our carry on compliant bags even though they met their requirements. As a result we missed our connecting flight and Alitalia had to put us up for another night in Rome. Worked out well but still an aggravation.

Mark, just to be clear it's not just size but weight restrictions. As said above, you need to check those for the airlines you'll be using.

You’ll want the smaller, “International” carry-on size if you’re traveling outside the U.S.A. We’ve only had to ever put bags inside the sizing temple once, to prove the bags were within the airline’s dimensions, but an American carry-on would’ve failed the test. This was in Greece, with easyJet.

You may not experience this on your Italy or Malta flights, but there are some airlines that not only specify the exterior length/width/height of a suitcase, but also the weight. In those cases, a bag that’s relatively heavy when empty, is really heavy when full.

Planning to wear a shirt more than once, and bringing a single, multi-purpose jacket helps keep overall clothes to a smaller amount, helping to get by with that smaller carry-on size for 2 months.

. . . After I typed all this, I discovered that Kathy just beat me to the carry-on weight topic. Definitely double-check with your airline for any limitations, or extra fees if you exceed them.

Some airlines limit carry on weight to 8 kilos. Not everyone can manage that. If you can't travel with the minimum weight and size on your airlines of choice, then just plan on checking something. Pack accordingly, with valuables in your personal item and a variety of luggage locks for peace of mind. It is just a part of being able to afford to travel. Yes, I get the pick up and go freedom of carry on only, but sometimes it is more of an inconvenience to try and contort one's self to that, than just to accept it.
Here's a June 2021 updated list at a glance. https://upgradedpoints.com/travel/airlines/carry-on-luggage-size-chart/
Of course, always double check your airlines' websites to confirm.

Op- let me explain it this way:

I once did a 3 city (really 4) trip from the US (SFO) to London, Eurostar to Paris, Paris to Rome, then Rome to London (BA, returned to London for the opening of an exhibition on Carrivagio I wanted to see) and then London back to NYCity. All air flights on BA.

I had no issues with my carry-on until I tried to board in Rome for the flight back to London. There my carry-on was checked- too big and over weight. The Italians said "no" and it had to be check-in. Same bag, same clothes, same airline. Now, my bag was clearly ok for the US-London International flight and return but not for the European domestic flights. Apparently no one cared at CDG but they sure did at FCO.

As my buddy Dirty Harry would say, do ya feel lucky?

As others have said, check your airlines. Lufthansa limits to 8 kilos, I know because they made me gate check my carry-on once. After that I bought a backpack that I knew would meet at least Lufthansa's size limits, and I weigh before I leave home.

Check the size, weight and number of carry ons for each airline you plan to use. Then pack for the most restrictive regulations. I have paid for one checked bag for the two of us, making one bag light enough for carry on. Watch Sarah Murdoch for packing light tips. If weight is an issue where your heaviest stuff to lighten the bag. Not paying for luggage has become a game for us.

Standard roller bags will be fine in most cases. It will also depend on the size plane you are flying for the jumps to Palermo, Malta, etc. Smaller planes will not allow roller bags as a carry-on regardless of size. Just hand bags. That is the same in the US. Take one of the locals/regionals and you cannot carry on a roller.