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)
Youth Small (6-8) - Light Blue1619.5
Youth Medium (10-12) - Light Blue1722.5
Youth Large (14-16) - Light Blue17.524
Youth XS (2-4) - Light Blue14.517.5