A bike helmet only offers adequate protection if it is properly adjusted. With this in mind, please choose the size that best fits your head and will be most comfortable.
To do this, it is best to measure your head circumference at the forehead level (where the diameter is largest), approximately 2.5 cm above your eyebrows and ears, with the help of a flexible measuring tape, as indicated below. If you do not have a flexible measuring tape, use a string or a shoelace which you will then be able to measure afterwards.