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Sector Nine Helmet Size Chart

Non CPSCHelmet Sizing
Head
Circumference

Hat Size

S

20 1/4"
52 cm

6 1/2

M21 1/4"
54 cm
6 3/4
L22 3/4"
54 cm
7 1/4

CPSC 
CE Certified
Helmet Sizing
Head 
Circumference

Hat Size

S/M

20" / 51 cm
20 7/8" / 53 cm

6 3/8
6 3/8

L/XL21 5/8" / 55 cm
22 3/8" / 57 cm
23 5/8" / 60 cm
6 7/8
7 1/8
7 1/2

Please note that CPSC helmets are adjustable because they come with extra padding pieces to customize fit.