Thanks for the question Rick.
You'll most likely want to size just a little bit over as opposed to just a little under. This way the plate cover won't slide around on your plate.
That said, this Cambro 909CW 9 3/4"" Clear Plate Cover is just a little small, and you'll want the 10 3/16"" Camcover. This way the outer lip of the plate cover will be over the outer lip of the plate. I've included it below for your convenience.
Answered on 5/20/2013 by Andrew Call from Boulder, CO