Most likely it would be 90. Hence the name 90, it should be a 90 inch head size. It's not like a K Six One 95 has a 100 head size.
Or another way to do it is measure it yourself. Get some kind of string, and line it throughout the inside of the frame in an "oval". The string should be touching the grommet where the strings are coming out. Measure the length of the string, then get a calculator. Divide that number by Pi (3.14), divide by 2, square it, then multiply by Pi. That would be your head size.
