United Airlines announced that they will only accept carry on bags that fit in the bag sizer. I say hooray! So often I’ve seen flights delayed as people try to jam their overstuffed carry on into the overhead bin. That takes away space from people who actually follow the rules but are boarding in a later group.
Just as an overview:
- Each airline has a different set of rules. Go to the airline’s website to make sure you comply.
- A bag with the expander zipper unzipped is never carry on sized. For this reason, I avoid bags with expander zippers. There is just too much temptation to pack more if you have an option to do so.
- Hard shell cases are unforgiving. This is another reason to select carry on bags that are soft sided.
- The outside dimensions determine the bag size, not the size of the luggage compartment. Wheelie people, I’m talking to you! Make sure the entire wheelie bag fits in the sizer. So often I’ve seen “carry on” bags on sale where the outer dimensions are larger than what is allowed. In order for a wheelie bag to fit, the luggage compartment will most likely be 2 inches (5 cm) smaller than the actual bag. Wheels take up space.
- If you must have a wheelie, look for bags that comply with international regulations. These are smaller, but they will fit in the overhead bin.
- All of the bags I recommend on my “Getting Started” page comply with US domestic carry on rules (except Spirit).
Ladies, we know that we can travel lightly with just a carry on. That means no bag expanders, no extra bags. Lets encourage others to pack lightly too – or check their bags.
Lady Light Travel 
Bravo! I have always wondered why the rules weren’t enforced and some people’s carrying appears to hold much more than my checked luggage can hold!
What about enforcement of not using other passengers’ overehead space?
Less bags on board certainly reduces the probability of that happening. That said, most airlines consider overhead space to be shared so no one can really claim it.
I wish I saw this enforced more often. Too many times I’ve been stuck gate checking my carry-on bag, because those before me have brought more than one carry-on bag, and stuffed all of the overhead bins. Or I’ve had my smaller bag removed from the overhead bin and been told to put it under the seat in front of me, so that someone else can put their luggage over my head. Both are highly aggravating scenarios.