It used to be whatever the "squared-up" and widest measurement was. For example, if a box is 30" wide, could you set the skull and antlers straight down inside it and and have it touch both sides? That'd be a 30" buck.
Take no shame in calling your buck a 27" buck. I have a 26 1/8" buck I killed in the Book Cliffs last year, and another 27 6/8" buck on my wall. I only refer to them as 26" and 27" wide... No need to fudge it anymore than that. They are both great bucks. Plus, all the "inches" that get used, I only use them as a reference to what a buck might look like.
One buck I chased with my bow in the Book Cliffs last year was a 170" 4x4. For most guys, that sounds like quite a nice buck. But, if I described the same buck by another of his measurements- "I chased a 20" 4x4 in the Book Cliffs" then suddenly a lot of guys are saying, that's not that big. Same Buck. My point is that even measurements don't tell the tale of the tape really... And they certainly DO NOT tell the tale of the adventure..!!
Nice buck my friend..!!
"Therefore, wo be unto him that is at ease in Zion!" 2 Ne. 28: 24