Helmet Size Head Size Inches Head Size Centimeters
XS/S 20-21.25  51-54
S/M 21-22.5  53-57
L/XL 22.5-23.5 57-60
XL/XXL 23.5-24.5 60-63

Measure your head.
To ensure a perfect fit, measure the circumference of your head at the height of the eyebrows and match it with the sizes above.

Check for a proper fit.
When trying on helmets, the helmet should be tight enough to stay in place on your head even without the chinstrap. If you nod or shake your head, the helmet shouldn't slide around. The front of the helmet should sit just about the eyebrows to protect the wearer's face.