The helmet size is in centimeters and to find out your helmet size, you need to measure the circumference of your head using tape measure and if you don’t have tape measure with you then you can use String and then measure length of the String.
Watch this video tutorial to learn how you can find your helmet size: https://www.youtube.com/watch?v=cDJ_7DvU5Aw
Size Table for helmets
The helmet size is measured by measuring the fullest part of the head, above the ears and the forehead and the back of the head. The range in cm shows your helmet size. Note that helmet sizes can vary between products.
|Head circumference in cm||49/50||51/52||53/54||55/56||57/58||59/60||61/62||63/64|