Each headwrap is sewn and hand-tied by mamas. Therefore, each size is approximate. Our size Small is made with newborns in mind and generally fits most newborns 0 to 5 months. Our Medium is made for babies and generally fits ages 5 to 18 months. Our Large is made for toddlers+ and generally fits ages 18 months to 6 years. Keep in mind each baby and child is different. We provide the circumference for you to reference as you shop for your child.