Inch Around	cm	Hat Size	Answer / KBC / MSR
19-3/4" - 20-1/8"	50-52	6-1/4 - 6-1/2	Childs S/M
21-1/4"	53-54	6-5/8 - 6-3/4	Childs L/XL
21-1/8"	51-52	6-3/8 - 6-1/2	XX-Small
21-1/4"	53-54	6-5/8 - 6-3/4	X-Small
21-5/8"	55-56	6-7/8 - 7	Small
22-3/8"	57-58	7-1/8 - 7-1/4	Medium
23-1/8"	59-60	7-3/8 - 7-1/2	Large
23-1/2"	61-62	7-5/8 - 7-3/4	X-Large
24-1/4"	63-64	7-7/8 - 8	XX-Large
24-5/8"	65-66	8-3/8 - 8-1/2	XXX-Large

Inch Around	cm	Hat Size	Apex/Vega
20-1/2"	53	6-1/2	XS
20-7/8"	54	6-5/8	XS
21-1/4"	55	6-3/4	Small
21-5/8"	56	6-7/8	Small
22"	57	7	Medium
22-1/2"	58	7-1/8	Medium
22-7/8"	59	7-1/4	Large
23-1/4"	60	7-3/8	Large
23-5/8"	61	7-1/2	XL
24"	62	7-5/8	XL
24-1/2"	63	7-3/4	XXL
24-7/8"	64	7-7/8	XXL
25-1/4"	65	8	XXXL
25-5/8"	66	8-1/8	XXXL

Inch Around	cm	Hat Size	Gmax	Fly	O'Neal
20-1/2"	53	6-1/2	XXS
20-7/8"	54	6-5/8	XXS	XS
21-1/4"	55	6-3/4	XS	XS
21-5/8"	56	6-7/8	XS	Small
22"	57	7	Small	Small	Small
22-3/8"	58	7-1/8	Small	Medium
22-3/4"	59	7-1/4	Medium	Medium	Medium
23-1/8"	60	7-3/8	Medium	Large
23-1/2"	61	7-1/2	Large	Large	Large
24"	62	7-5/8	Large	XL
24-3/8"	63	7-3/4	XL	XL	XL
24-3/4"	64	7-7/8	XL	XXL
25-1/8"	65	8	XXL	XXL	XXL

Inch Around	cm	Hat Size	HJC / Shoei / Aeon
19-3/4" - 20-1/8"	50-52	6-1/4 - 6-1/2	Youth S/M
21-1/4"	53-54	6-5/8 - 6-3/4	Youth L/XL
21-1/8"	51-52	6-3/8 - 6-1/2	XX-Small
21-1/4"	53-54	6-5/8 - 6-3/4	X-Small
21-5/8"	55-56	6-7/8 - 7	Small
22-3/8"	57-58	7-1/8 - 7-1/4	Medium
23-1/8"	59-60	7-3/8 - 7-1/2	Large
23-1/2"	61-62	7-5/8 - 7-3/4	X-Large
24-1/4"	63-64	7-7/8 - 8	XX-Large
24-5/8"	65-66	8-3/8 - 8-1/2	XXX-Large

AFX, AGV, GREX, Icon, M2R, MDS, Moose, Nolan, Suomy, Thor and Z1R helmet fit guide

AFX, M2R, Thor and Z1R youth helmet fit guide

FOX Men's and Youth helmet sizes
HELMET With tape level, measure the widest point of your head, approximately 1 inch above your eyeborws.