I looked all over the web and couldn’t find this info. For future reference sake, here are some standard metric canvas sizes found here in Japan. I believe it’s the same for Europe as well as I recently attempted to copy a Renoir and what do you know, the original was “exactly” F15 measurements! The more I am forced to deal with metric, the more I am liking it I must say!
Standard Canvas Sizes (unit=millimeters)
size F3 275×220
size F4 333×242
size F6 410×318
size F8 455×380
size F10 530×455
size F12 606×500
size F15 652×530
"Kabukicho Flowers & Night"- F10 Oil on canvas.