| How to Measure Your Head for a Helmet|
Before you begin, you'll need a soft fabric measuring tape with centimeter increments. The centimeter measurement is important, as this small unit enables you to get the most accurate measurement of your head.
Note: Some manufacturers use head circumference in centimeters for their helmet sizing, some use hat sizes, and some use universal helmet sizing in extra small, small, medium and large. Additionally, helmet sizes vary between manufacturers.
3) Place the helmet level on your head. Be sure to try on helmets with your hair in the same style in which you ride. If you have long or thick hair that you wear under your helmet, you may need to increase your helmet size slightly.
Note: Attempt to make your hair as flat to your head as possible when wearing your helmet; many people prefer to use two hair nets to obtain a sufficiently flat, snug fit. The first hair net is tied into the ponytail, and the second hair net holds the ponytail flat to the head. For illustrated how-to details, see the topic Helpful Tips for Hairstyling.
4) Check the helmet shape.
Some helmets suit round heads and some suit oval heads; you may have to experiment with different brands to find the most suitable helmet. There are various ways to determine whether a helmet is the wrong shape for your head, but here are some examples.
If the helmet squeezes your forehead but rocks easily sideways, it is too round for your head. If the helmet fits the sides comfortably but rocks front to back, it is too oval for your head.
A correctly sized helmet sits down snugly on your head and covers your entire skull with equal pressure all around. No gap exists between your helmet and your head; even pressure with the lining allows the helmet to absorb force in an accident.
If you feel the helmet wants to rise or pop upward from your head, then it is too small. If the helmet is loose all around your head and sitting low on the eyebrows, it is too large.
While a slightly large helmet may feel very comfortable initially, if you select one that does not fit snugly when it is new, it will become too large over time as the lining breaks in. A large helmet will shift during riding, could become a distraction and will not protect you well during a fall.
If you are trying on an adjustable helmet and the fit is very close to being correct, you might tighten it through the use of slides, dials, changeable padding or ties, and repeat these tests. Otherwise, try another size, style or brand of helmet.