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
"Shimbashi Dori" - 53 cm x 65 cm (F15) Oil on Canvas