sidewall bulge measurement ?

Well I know. 325cms/25.4cms per inch = 12.8 inches section width on a specified rim.I dont remember the rim size for that. It mighta bin a 8.5, cant say. Also the section is not always exact.
My BFG-325s are 13.2 inches on a 10 inch rim. the aluminum rim is actually 11 inches outside to outside,so; (13.2 - 11)/2 = 1.1 inches of bulge. pretty much the same as Trebligs. Mine are measured at 24 psi. My 325s are 27.9 tall IIRC. Mine fit inside the wells on a narrowed rear, under a Bcuda. Just BARELY.
BTW; most/maybe all, tire manufacturers have these specs printed up in their tire catalogs, as was earlier mentioned.