Originally Posted by UAX@SFO

I respectfully note that there are no SkyWest (or any United Express, for that matter) gate agents in Chicago/O'Hare. All ground handling of United Express flights at O'Hare are handled by United mainline employees.

To be honest, it's difficult for me to gauge carry-on sizes as well, and I've been doing it for over 5 years now. I see them in all shapes, sizes and colors. I fly our aircraft fairly often and am familiar with storage capabilities on board. However, generally in SFO if a passengers says it will fit, we will take them at their word and let them board with it. If it doesn't fit, then we'll check it. Let the customer try first and let them have the option then afterwards.

Happy Travels!