To check the head size, use a measuring tape. Use the centimeter side of the tape, and place the tape one inch above the eyebrows. Measure the circumference of the head. Check the centimeters on the measurement tape. Check the size chart to know your size category.  Using this method, you can know your head size accordingly and buy the perfect helmet for yourself. HELMET SIZE CHART IN CMS All Vega Brand (adult series)XS – 54 cmS – 56 cmM – 57 cmL – 58 cmXL – 60 cmXXL – 62 cm All vega Brand (Kids Series)2XS – 52 cmXS – 54 cmS – 56 cm