What size carry on for both domestic & international flights?

Airlines can have different requirements, so if you want ONE piece to use for mostly domestic travel, then 9x14x22, as it'll be fine for most overseas travel. Some of the low-cost carriers you might take for a connection in Europe can have smaller requirements.

It is so confusing. I suggest you look at the sizes for the airlines you are likely to fly.

I recently bought a new bag, a spinner. I looked at the airlines I usually fly, particularly Delta and British Airways. The smallest measurement was 14 x 9 x 22 inches. That's what I chose to go with via a Maxlite 5 compact spinner, which is 5.1 lbs. It is truly this measurement, many others falsely advertise and are too large. In fact this one might even work for international as the handle just barely brings it up to 22 inches and the handle will squish down to a smaller measurement. I usually have no qualms checking my bag, but I would be hesitant checking this one until I've thoroughly tested it due to it's lightness.

I would also think about buying a bag in Europe that fit the European height requirements if you really want to be sure. I find the ones with the correct European height, which are sold near me, make up for the decrease in height by making the width too wide, like some of the Maxlight 5 bags at over 15 inches wide. Even Rick Steve's spinner is 10" deep, therefore too deep.

Good luck. Enjoy the search!

Edit to add:

... ones with the correct European height ... make up for the decrease
in height by making the width too wide ... .

Not too many years ago, the European standard was 55x40x20 cm (21.65"x15.75"x7.87"). Some airlines, like Lufthansa and SAS, have stayed with 55x40, but increased the thickness to 23 cm (9"). Others, most noticeably British Air, allow 25 cm (9.8", almost 10").

The domestic regulation size bags (22"x14"x9") have 2772 ci capacity. If you got a 55x40x23 cm bag (the maximum size on Lufthansa), you'd have 3087 ci of capacity. As long as you only took direct Lufthansa (or SAS) flights to Europe, you could use that bag with 11% more capacity.

I see the rules and regulations about carry on luggage has
changed/updated.

Not as far as I can see based on looking at the airline websites today. Where did you see that?

I just checked (once again) the carry-on baggage limits for American, Delta, United, Air France, British Air, KLM, Lufthansa, and SAS. I don't see any change from say, a year ago.

In all cases, 21.6"x14"x9" would fit on any of those 8 airlines.

22"x14"x9" would fit on any of the domestic ones and for British Air.

Except for British Air, the other four European airlines limit the height to 21.6" but allow more width (15¾" to 18") or thickness (9.8").

21.6”x14”x9” is 2722 cu. Inches or 44.6L. The cloth material of the bag has volume and can subtract 100 -200 ci from the volume. Wheel clearance for spinners can easily subtract 200-300 ci. Rounded corners, tapered bags, the handle tunnel, and pockets that use thickness but don't fill the height x width all subtract from volume.

According to a study done several year ago by Consumer Reports, most bag advertised as meeting carryon size requirements don't, the major sin being they ignore wheels and handles, which airlines include.

I also recommend you look at the metric measurements for luggage and for the airline requirements. I am NOT a metric person, lol, but I found when I was searching in 2022 that many luggage companies round up or down to get the inch measurement. It was not consistent as to which way they rounded. All measurements should include wheels/handle/side or front pockets.

I'd go for a 55cm X 35cm X 25 cm bag and as lightweight as you can find.

Not sure what airline you might fly on but here is Air France's baggage requirement:

https://wwws.airfrance.us/information/bagages/bagage-cabine-soute#dimensions

Here is the link for Delta's rules:

https://www.delta.com/us/en/baggage/carry-on-baggage

IF you are flying a combo of 2 airlines, expect to go by the rules of each carrier. For instance, Delta is more generous but if you are connecting to an Air France flight you might find your luggage sized and weighed for the onward leg.

When it comes to airlines and your bags, "one size fits all" is NOT a real thing - unless you are going to go by the absolute smallest item size-limit for any airline you will ever fly - and IME, just after you commit to that, you will soon be contemplating some small, obscure airline you had never heard of previously, and will be shocked, SHOCKED at their tiny limits which will be even smaller than your smallest bag. Accept that there is no universal standard for size (and don't forget about weight, too).

My strategy is to have a variety of bags, in a range of sizes, to choose from, and pick what works for that airline on that trip.

IME the "Rick Steves Rolling Carry-on" bag is a good option that often (though not always) meets the requirements for carry-on size for most European airlines, including most LCCs (low cost carriers, the impossibly cheap ones). We bought two of those and we are mostly happy with them (even though I brought one back to the Rick Steves HQ in Edmonds to return it when some stitching started to pull off after a single, gently-used trip, and they declined to offer a replacement contrary to their their guarantee). But on some airlines, you may need an even smaller bag to pass muster. Those bags are out there, do a search on amazon for "carry-on bag" + the name of your airline, you will find plenty to choose from (but don't believe what the sellers tell you are the bag size limits for your airline, check that yourself).

I've now got a half-dozen different bags to choose from, which range from small to very small. Of course, next time I plan a trip, I expect I will need one just a bit smaller to add to my collection (admittedly, I do occasionally fly on pretty obscure little airlines, and most folks here probably don't need to meet the same requirements).

Bottom line: there is no universal standard. It all depends on the airline and many other variables which can not be accurately predicted (eg the mood of the gate staff on the day you fly).

You should look at the requirements of the airline you are flying and purchase accordingly, and ignore all other advice.

I generally fly United and have a carry on bag that meets their requirements. On the rare occasions that I have traveled by air within Europe I just check my bag so I don’t have to worry about meeting their stricter requirements. It doesn’t cost that much extra on Ryan Air and Easy Jet.

I am committed to two-wheeled suitcases, because the wheels are more tucked in, and I don't lose precious inches to wheels. Two- wheeled are hard to find anymore, but sometimes I search for "wheeled duffle bags" and find them. Admittedly, I don't need any more carry-on suitcases, but it's always fun to look.
I agree, many stated measurements are not accurate. Maybe one trip I'll shop too much and be forced to buy a carry-on in Europe with European dimensions.
Safe travels.

In October we flew Swiss from San Francisco to Zurich (RS Ravenna carryons fine); connecting on Swiss to Venice (RS carryons had to be gate checked, too big and it wasn’t because overhead bins were small, they were large and basically empty, they had all been gate checked)…….you definitely need to check with the airline you’re flying with and whether their international flight bag limits are the same as their inter European flight bag limits. I remember looking at what Swiss allowed as carryons on their inter European flights and thinking there was no way I could travel for 3 weeks with that size bag no matter how efficiently I packed. The feeling is that the airlines seem to be downsizing to the point we are going to have to check our bags. I do have to admit that boarding and deplaning went quite quickly and efficiently. So….

100% agree with taking a tape measure and checking the actual dimensions of any options you’re considering. I found some of them to be out of compliance as carry on size & with their own specs.

Another thing to consider is flexibility in the suitcase/bag. I own a Cotopaxi Allpa 35L. The specs state it’s 22x12x10”. But when I measure mine before packing, it’s 20x12x6.5” because of the flexibility. So if I know I’m going on an airline that has tighter specs, I need to pack accordingly. I had a similar benefit with my former 2-wheel bag which had a completely flexible front. That’s how you could use one bag in different conditions.

Why do people stress over this?

Most US airlines let you carry on about anything. That is fine for the way over. Beyond that, look at the various requirements, and if they are miniscule, then JUST CHECK A BAG, it won't kill you, and the cost is miniscule. Your peace of mind is worth it alone.

A good example, on about every other trip (of one to two a year) I fly Ryanair. Yep, that is the scary airline that charges you for everything, strictly checks bags and fines you, charges you to check in at the airport if you have no boarding pass...but they are a great airline to fly.

So when I fly Ryanair, I opt for the Plus package, which gives me airport check-in (in case I have a problem), an assigned seat, and a checked 20 kilo bag, which covers any light packer. The otherwise 10 kilo limit is on the ragged edge of most travelers from the US, besides the size requirements, plus many also have a hefty "day bag"

The cost? Still cheap. But many can't get past the fact that they could get a 25 euro plane ticket and not check bags, or pay 50 euro and check. News Bulletin: 50 euro is still dirt cheap. Plus checking a bag on a point to point flight is virtually no risk.

So figure out the flights that work best for your schedule, then just follow the rules laid out. If you can travel in a purse and 5 kilos of weight, no problem, if not, consider paying for what you need.

I also like the Max Lite. Remember that some European airlines also have weight restrictions, so the less your empty bags weigh, the more things you can pack in them.

Response to a question: I pack light and small so I can manage my bags easily and so I am not an easy target. I am a senior woman who travels solo. The lighter my bags, the more confident I feel getting on planes, trains, and subway or walking through town, etc. Packing light and not checking a bag are two different things. I usually check my carryon bag, particularly when it's free; ie, Delta gate checking or BA is always free. However, having the option not to check my bag is very important, IMO, so I can change on a dime and not check my bag...think weather delays, etc. This makes it easier for me to get a different flight as my bag is not in the belly of the plane. For my new bag, I need to test its rigidity before I check it.