Framed, I'd like your art to be at least half the width of the credenza and at least that high or higher. You could also use a pair of pieces or 4 or 6 pieces. I don't know of any set rules.

Thank you so much.

Don't go larger than 3/4 the length of the buffet. It can also depend on what else you want to include on the buffet.

In my comments, I was talking about vertical or square pieces. It's certainly fine to use a horizontal piece that is not as tall as it is wide, such as you see below. I would not advise using a piece wider than the buffet, but as long as it's a little bit narrower than the buffet, I don't mind.



https://www.houzz.com/photos/2014-birmingham-gbahb-ideal-home-craftsman-dining-room-birmingham-phvw-vp~11156759