How to find your size ?
Please use a cloth tape to take your measurement. It is better to have a helper do the measuring in order to get accurate measurement. The circumference of the head should be measured at a point approximately one inch above the eyebrows, or at whatever point gives the largest possible measurement. If you find that your measurement falls between two sizes, choose the smaller size for this helmet.

XS - 20 1/4 - 20 7/8" ( or 52-53 cm) 
S   - 21 - 21 5/8" ( or 54-55 cm) 
M   - 21 3/4 - 22 3/8" ( or 56-57 cm) 
L    - 22 1/2 - 23 1/8" ( or 58-59cms) 
XL  - 23 1/4 - 24" ( or 60-61 cm) 
XXL - 24 1/8 - 24 7/8" ( 62-63 cm) 

Features

• Super Light Weight: Approximately 30 oz
  
  
• Dimensions: 8.5 inches from ear to ear and 10.5 inches from front to back
  
  
• EPS Liner Thickness : Only 1 inch
  
  
• Fabric Helmet Bag and Owners Manual included
  
  
• Quality Plush Interior
  
  
• Removable visor
  
  
• Face Shield Compatible(Compatible with 100Shield)
  
  
• You can easily wear glasses with or without the face shield
  
  
• Stainless Steel Dual D-rings
  
  
• DOT clear coated in the back
  
  
• Great quality materials and workmanship