'rjw' you are making an awful big assumption there and you know what happens when you assume. You are assuming that the all 6 or 12 of those rackets started out at the same length. I doubt that is true. That would probably only be the same if they came out of the same mold and the butt capps were all put on the same.
Just measure the Head of the racket inside to inside or outside to outside.
I would like to apologize to anyone I have not offended. Please be patient I will get to you shortly.