Size Description Premmie For Premmie babies. Newborn 0 to 3 Months XSmall 3 to 6 Months Small 6 to 12 Months Medium 12 to 18 Months Large 18 to 24 Months 2T 24 to 36 Months 3T 36 to 48 Months 4T 48 Months to 5 year old XLarge 5 to 6 year olds XXLarge 6 to 8 year olds