Hello
Generally, we do not measure sections of prints. Sorry we no longer pull out the prints to check each individual
requests of this nature as we get too many requests and this constant pulling out
of the prints damages and creases the artworks.
That said, It is approximately 24", but don't hold us to it. It is always best you wait until you recieve any artwork before you start measuring any mattes or frames as this only creates problems if measurements are not precise. Thank you.