How big is 45 linear in or 115 cm (L+W+H)?
 

My sister is leaving for HKG on CO Thursday (I am on AA/CX) and she has asked me if she can take her small carry on suitcase with her on her flights.
The CO site says 45 linear in or 115 cm (L+W+H) but we cannot figure out what the heck that means.
Is that a standard 20 or 21 inch rolling bag?
I have no clue... and I only carry a backpack on flights.

You just have to measure your bag and add up the L + W + H numbers. You can't say that all standard 21 inch bags are the same because some are fatter or thicker than others. 21 inches just refers to the length.

Thanks! Hahahaha! The (L+W+H) was the formula but I just didn't 'see' it :)

BUT -- the measurements have to include the wheels and handle. It the airline uses a sizing box, a lot of wheeled bags will fail because the wheels and handle extended beyond the limits of the box.

CO has put sizers at many of its gates, including basically all at EWR and IAH. They don't necessarily use them, but they are there. So, not only do the piece has to be within 45in (down from 51 before), but they also can't be larger than 22 x 14 x 9.

Now, if she's only flying EWR-HKG, then it shouldn't be a problem as the bins on the 777 are huge and carry-ons are never a problem even on a full flight. And if she's connecting from a regional jet or turboprop, then also no problem as she'll be gate-checking anyways. But if she's connecting from a domestic mainline 737 or 757, AND that flight is full or mostly full, then they may indeed ask the passenger to fit the carryon in the sizers before letting them on.

Anyways, is she really going to HKG just with carryons?

She is using that carry on instead of a backpack... and to carry emergency clothing and such should her bag fail to make it to HKG.
I encouraged her to take just a duffle, but she wanted something with wheels.