I searched through the NHL rules, and I read a couple of sports articles, and I couldn’t find anything that specified the maximum size that a goalie’s glove could be.
I’ve seen some goalies whose glove seemed pretty darn big, as if they were made for catching grapefruits rather than pucks. It seems like some goalies [sub]cough[/sub][sup]Belfour[/sup][sub]cough[/sub] have gloves that are exceedingly large.
See the NHL’s Rule 21 regarding restrictions on Goalkeeper’s Equipment. The page details maximum size for goalie equipment and gives measurement procedures as well.