Like previous Purebaby swim hats, this one has the same consistent sizing. Size large fit my then 2yo well. She is now 4yo and it still has room for growth. Have always been able to wear it over her ponytails/buns as well due to the stretchy swim fabric. No need for a ponytail hole. Been through many trips to the beach and in the washing machine. Bought this as a spare to mix it up. Very fast shipping too. Thank you.