The average dinner plate today is 11.5 inches. Fifty years ago, it was 9.5in. A hundred years ago, it was 9 inches. In the 1700-1800s, it was 8 to 8.5 inches. For centuries before that, the common "trencher" was 4-6 inches square. And say ~2000 years ago, food was served for the entire dinner party on a single 12-16inch communal platter.

Dinner plates have gotten huge, historically speaking.