Industry standard for baby and toddler apparel is to use age as the size, however we do recommend measuring a child as it is possible to have an older child that needs a smaller size, or vice versa. For example, a baby that is 14 months may still be wearing a size 6-12 month given his or her other measurements. If your childs measurements fall between sizes, we recommend sizing up to ensure a better and longer lasting fit. Please refer to the chart below for measurements: