This extraordinary frame glistens and gleams even though it's over 120 years old! Keep in mind, there were no standard sizes in the 1800s. Everything was custom made. Inside the rabbet is 39 1/4" x 20 3/8". That's the maximum size that will fit in the frame (although if your piece is very slightly larger you could have it routed out, say for a 40" x 20") The sight is 38 3/4" x 19 7/8". That is what will show when your piece is fitted as is. The rabbet (lip) is narrow- only about 1/4". Outside dimensions are aprox. 46" x 27". So, a mirror can be easily cut to size, but if you are framing artwork, you will likely have to adjust either by making the piece custom to fit the frame or, if it is smaller, having a liner fitted by a local framer. But it will be worth the effort. What a great frame. FREE SHIPPING! Please note: The frames I sell are true antiques or vintage items in as-found estate condition. Nicks, repairs, oxidation, etc. are common and should be expected. Please examine photos carefully.