To determine the correct helmet size, wrap a measuring tape around your head, keeping the tape just above the ears and level front to back.
 

Snow Helmets

Adult Helmet Sizing Size (cm) Size (in)
M 54 - 58 21.26 - 22.83
L 58 - 62  22.83 - 24.41
 
Youth Helmet Sizing Size (cm) Size (in)
One Size 52 - 58 20.47 - 22.83

Bike Helmets

Lookout Helmet Sizing Size (cm) Size (in)
M 54 - 58 21.26 - 22.83
L 58 - 62  22.83 - 24.41
 
Jib Helmet Sizing Size (cm) Size (in)
M 55 - 58 21.65 - 22.83
L 58 - 62  22.83 - 24.41