Using a tape measure or length of string; the head should be measure at a point approximately one inch (2.54 cm) above the eyebrows, horizontally around the largest part of the head. The measurement should be taken several times to confirm the largest measurement.
Refer the measurement to the sizing chart.
If measurement is between helmet sizes opt for smaller size.
The helmet fit should be ‘firm’ but not uncomfortably tight (with use the fit may relax slightly).
The top of the head should be in contact with the helmet interior.
The chin should not be in contact with the front bar.
Cheek pads should make light to medium contact.
There should not be any space between the forehead & the helmet interior.
When moving the helmet side to side & back & forward, the helmet should move the skin on the head & face.
With the strap fastened check the helmet cannot be ‘rolled off’ by pushing from the back then from the front.
Finally ensure the field of vision is not obstructed.