Inches, McCurry sells as large as 40x60 inches, so roughly 100x150cm.
Here's an article I read this morning that demonstrates what I'm saying. It's from a different industry, my wife's a programmer, the process shown for developing a salable product is just as valid for photographers as it is for programmers.
There are a variety of examples in photography too. The f/64 group of Ansel Adams et al, created a product style that the group adhered to in order to get more gallery time for its members. See their manifesto.