How do I know what size I need for my helmet?

How do I know what size I need for my helmet?

The sizes are given by the measurement of the cranial perimeter. You can use a tape to measure this perimeter and compare it to the helmet’s specifications. Closca Helmet Classic is available in three sizes, S,M and L Closca Helmet for Kids is available in one size, S Closca Helmet Loop is available in two sizes, M and L