Helmet Sizes
Use a tape measure to measure the circumference of your forehead at the position you want the helmet liner to rest.

Forehead Circumference in Inches
Helmet Size
Forehead Circumference in Centimeters
20 1/4 - 20 7/8
X Small
51 - 53
21 - 21 5/8
Small
53.3 - 55
21 3/4 - 22 3/8
Medium
55.2 - 56.8
22 1/2 - 23 1/8
Large
57.2 - 58.7
23 1/4 - 24
X Large
59 - 61
24 1/8 - 24 7/8
XX Large
61.3 - 63.2

Note-If you don't have a tape measure, you can use a piece of string. Wrap the string around your forehead about where you want the helmet liner to rest. Then use a ruler or yard stick to measure the string!