The circumference of the head should be measured at a point approximately one inch above the eyebrows in front, and at a point in the back of the head that results in the largest possible measurement. Take several measurements, to make sure you have the largest one.

PLEASE NOTE THAT THIS IS AN APPROXIMATE GUIDE AND NOT EXACT. THE SHAPE OF YOUR HEAD IS AS IMPORTANT AS YOUR HEAD MEASUREMENT WHICH MAY AFFECT FINAL FIT!

Bell Helmets
INCHES
SIZE
METRIC(cm)
19 3/4
6
Youth S/M
50-51
20 1/2
6 3/8
Youth L/XL
52-53
21 1/4
6 3/4
XX-Small
54
21 5/8
6 7/8
X-Small
55
22
7
Small
56
22 3/8
7 1/8
Small/Medium
57
22 3/4
7 1/4
Medium
58
23 1/8
7 3/8
Medium/Large
59
23 1/2
7 1/2
Large
60
23 7/8
7 5/8
Large/X-Large
61
24 1/4
7 3/4
X-Large
62
24 5/8
7 7/8
XX-Large
63
25
8
XXX-Large
64
25 3/8+
8 1/8+
XXXX-Large
65+

Fox Racing Helmets
INCHES
SIZE
METRIC(cm)
18 3/4 - 19 5/8
Kid's Small (KS)
19 1/4 - 20
Kid's Medium (KM)
20 1/8 - 21
Kid's Large (KL)
20 1/2 - 21 1/8
X-Small
21 1/4 - 22 1/8
Small
22 3/8 - 23 1/8
Medium
23 1/4 - 23 3/4
Large
22 7/8 - 24 3/4
X-Large
24 7/8 - 25 3/4
XX-Large

Fox Helmets
INCHES
SIZE
METRIC(cm)
21 1/2
X-Small
22 1/4
Small
23
Medium
23 3/4
Large
24 1/4
X-Large
24 3/4
XX-Large

HJC Helmets
INCHES
SIZE
METRIC(cm)
20 - 20 1/2
XX-Small
52-53
20 7/8 - 21 1/4
X-Small
53-54
21 5/8 - 22
Small
55-56
22 1/2 - 22 7/8
Medium
57-58
23 1/4 - 23 5/8
Large
59-60
24 - 24 3/4
X-Large
61-62
24 3/4 - 25 1/4
XX-Large
63-64
25 5/8 - 26
XXX-Large
65-66

Icon Helmets
INCHES
SIZE
METRIC(cm)
21 1/8
XX-Small
53
21 1/4
X-Small
54
21 5/8
Small
55
22 3/8
Medium
57
23 1/8
Large
59
23 1/2
X-Large
60
24
X-Large/XX-Large
61

One Helmets
INCHES
SIZE
METRIC(cm)
20 7/8 - 21/14
X-Small
53-54
21 3/8 - 22
Small
55-56
22 1/8 - 22 7/8
Medium
57-58
23 1/8 - 23 7/8
Large
59-60
24 - 24 1/2
X-Large
61-62
24 5/8 - 25 1/2
XX-Large
63-64

Shoei Helmets
INCHES
SIZE
METRIC(cm)
20 1/2
XX-Small
52
20 7/8
X-Small
54
21 1/4
Small
56
22 1/4
Medium
58
23
Large
60
23 7/8
X-Large
62
24 1/2
XX-Large
64

Suomy Helmets
INCHES
SIZE
METRIC(cm)
20 1/2 - 20 7/8
X-Small
53-54
21 1/4 - 21 5/8
Small
55-56
22 - 22 1/2
Medium
57-58
22 7/8 - 23 1/4
Large
59-60
23 5/8 - 24
X-Large
61-62
24 1/2 - 24 7/8
XX-Large
63-64
25 1/4 - 25 5/8
XXX-Large
65-66

Thor Helmets
INCHES
SIZE
METRIC(cm)
20 1/2
XX-Small
52
20 3/4 - 21 1/4
X-Small
53-54
21 5/8 - 22
Small
55-56
22 1/2 - 22 3/4
Medium
57-58
23 1/4 - 23 5/8
Large
59-60
24 - 24 1/2
X-Large
61-62
24 3/4 - 25
XX-Large
63-64

Thor Youth Helmets
INCHES
SIZE
METRIC(cm)
20 5/8
Small
49-50
21 1/8
Medium
51-52
21 1/4
Large
53-54
21 5/8
X-Large
55-56

Troy Lee Designs Helmets
INCHES
SIZE
METRIC(cm)
21 1/4 - 22
Small
54 - 56
22 - 22 3/4
Medium
56 - 58
22 3/4 - 23 5/8
Large
58 - 60
23 5/8 - 24 1/2
X-Large
60 - 62