Can someone help me find the right specs for my 240?

I thought i had it all figured out last night. After measuring the wheels in the picture and finding their offset i simply used willtheyfit.com to find the new specs. However, the wheel builder has informed my that you do not measure from outside lip to outside barell, but instead from the inner bead to bead. To find width that is.

So can i just take 1” off my measurements and be right? I feel like it should be straight forward math but i’ve never built wheels before.