Filmsize question

I was just wondering if the filmsizes for sheetfilm like 8x12" and 20x24" is the outer measurement or the size of the picture area ? I am wondering because I have seen two different sizes on 8x10 film on some website.

It's neither!

The sheetfilm size is the size of a glass plate negative of that nominal size. When film was introduced, the size was shrunk by a few mm to fit in film sheet sheet-metal adapters.

This has led to curious things like 13x18cm film being nominally almost exactly 5 inches by 7 inches, while 5x7" film is a few mm smaller...

Is there a list somewhere that is a reference for the outside measurements of sheet film ?