Micro Helmet Elephant Small (18-20.5 inches) Small: 48  53cm (about 18.9  20.9 in) Complies with ASTM standards for Bicycle Helmets as required by the U.S. CPSC To determine sizing: measure all the way around your child's noggin, just above the eyebrows Always measure your child's head before ordering-- safety first! A helmet that is an inch too big/small will not offer protection