This new Sesame Street set is perfect for your baby's birthday party, photo shoot, or cake smashing party! This set includes a diaper cover, tie, and personalized birthday hat! The hat is a one-size-fits-all hat, and is modeled after a standard party hat, with elastic chinstrap. The hat is covered with fabric to match the party outfit! The measurement sizes for this diaper cover set 12-18 months are: Leg is 9 1/2" and can stretch to 11 1/2". The waist is 16" and can stretch to 19". If you have any other questions about measurements, please don't hesitate to ask.