Sizes and measurements. Children The basic rule regarding the hats & headbands for children is that the size of the hat corresponds to the age of the child. Example: Size 2 is usually suitable for a 2-3 year old and a size 6 is for a 6-7 year old. Measurements are in centimeters Size 1 Size 2 Size 4 Size 6 Size 8 50-51 cm 51-52,5 cm 52,5-54 cm 54-55,5 cm 55,5-56 cm Measure around the largest part of the head, just above the eyebrows.   Adults Measurements are in centimeters Small Medium Large 56-57 cm 57-58 cm 58,59 cm Measure around the largest part of the head, just above the eyebrows.