Hold the end of a non-stretch cloth measuring tape. If you do not have a cloth measuring tape, use a piece of string that does not stretch.   Wrap the measuring tape (or string) around your head returning to the starting point.  The measuring tape should rest above the ears, and the eyebrows.  Write down where the measuring tape meets.  If you used string, carefully measure with a tape measure.   Make sure the measuring tape (string) fits snug, but not too tight.