Measurement

• Helmet sizes are measured by the circumference of your head. In order to find the correct size, measure your head by placing a tape measure around it. Sizes typically range from 48 to 62 centimeters (18 7/8 to 24 3/8 inches).
  
  

Shapes

• As with shoes, not all helmets fit in the same way. Some helmets are designed for oval heads, others are designed for round heads and some are geared toward people with a mixture of the two. Find one that is the right size and shape for your head.
  
  

Fitting

• Place the helmet on your head and hold the straps until it fits well. There should be no excessive gaps between the lining and your head, nor should the back of the helmet touch the nape of your neck. The helmet should fit tightly and not move if you shake your head.