Step 1 Measure Yourself!
You're going to look pretty goofy doing this. Just a heads up.
Take your tape measure and wrap it around your head (not too tightly) at the widest part, where the bottom edge of your hat will most likely rest. For many people, this would be about a half an inch above the eyebrows, or about one-eighth of an inch above the top of the ears.
Hold your thumb or another finger against the tape measure where it comes around to meet the end. Take a look at the measurement you come up with. Congratulations – you now know the circumference of your own head! Be sure to write down your measurement in inches, and if your tape measure has metric units on it, go ahead and write down your measurement in centimeters, too.