Measurement
Size
Metric
20-1/2
6-1/2 (XXSmall)
52
20-7/8 to 21-1/4
6-5/8 to 6-3/4 (XSmall)
53-54
21-5/8 to 22
6-7/8 to 7 (Small)
55 - 56
22-3/8 to 22-3/4
7-1/8 to 7-1/4 (Medium)
57-58
23-1/8 to 23-1/2
7-3/8 to 7-1/2 (Large)
59-60
23-7/8 to 24-1/4
7-5/8 to 7-3/4 (XLarge)
61-62
24-3/4 to 25-1/8
7-7/8 to 8 (XXLarge)
63-64
25-1/2 to 26-1/4
8-1/8 to 8-3/8 (XXXLarge)
65-67
For a perfect fit...
NOTE: Although many people's heads may measure identically, they may be shaped differently which affects size and fit. After you have selected the proper size, when you recieve your helmet it should have a snug, but comfortable fit for optimum performance.