Choose a hat that is right for your head size. You can measure your head circumference by wrapping a measuring tape around your head so that it runs across the middle of your forehead and just above your ears (not across your ears). Much like shoe size, the circumference is unique to a person and does not change for adults. You can measure your child’s head circumference the same way or check it from your child’s medical records.
These are the typical sizes for adults and children:
Women 55–59 cm (21.5–23 in)
Men 56–62 cm (22–24 in)
Children 48–56 cm (19–22 in)
Toddlers 38–48 cm (15–19 in)