Width is measured across the chest below the sleeves from seam to seam. Height is measured from the bottom of the shirt to the highest point on the shoulder (where the seam meets the neck).

Please note that each product has its own specific sizing chart.
SizeWidth (inches)Height (inches)
Infant 12M - Light Blue9.512
Infant 18M - Light Blue10.513
Infant 24M - Light Blue1216
Infant 6M - Light Blue8.511