47cm - 1/2 years
49cm - 2/3 years
51cm - 3/4 years
53cm - 4/5 & 5/6 years
55cm - 6/7 & 8/9 & 10/11 years
56cm - 12 years plus

These are all standard sizes. We recommend that you measure the head of the child, teenager or adult. Circumference of the top of the head just above the eyebrows.