Originally Posted by
exerda
I have had non-UA staff insist I use the sizer (e.g. the AirServ guys while waiting in a TSA line!).
Funny, the only time I've ever been asked to use one was in Prague, in the LH sizer, not even UA.
Still, for the OP, if your bag is grossly over the allowed size, save yourself and your fellow passengers some trouble (or time) and just check it. If it's close, don't worry about it.