Size chart - headgear

Head circumference in centimeters Letter case Age
Less than 40 cm XS Newborn
40 - 42 cm S 3 to 6 months
44 - 46 cm M 6 to 12 months
48 - 50 cm L 1.5 to 5 years
52 to 54 cm XL 5 to 8 years
56 to 58 cm XXL + 8 years and adults

The age recommendation is indicative, you can ensure the best fit by measuring the head circumference.