|Inches||20 ⅛ - 21||9||3 ½||9||4|
|Cm||51 - 53.5||23||9||23||10.2|
Measure your head circumference with a non-stretchable measuring tape. Place the end of your tape on your forehead and wrap the rest around the back of your head, keeping it 1″ (2.5 cm) above your ears. Pinch the spot where the tape meets the other end, lift the loop over your head, and note the measurement. Be as careful as possible to get the most precise measurement.