T-Shirts

A Length
Place the end of the tape measure next to the collar at the top end of the T-shirt (highest point of the shoulder). Pull the tape measure down to the bottom end of the shirt.
B Width
Place the end of the tape measure at the seam under the sleeve and pull the tape measure across the shirt to the seam under the opposite sleeve.
C Sleeve Length
Place one end of the tape measure at the top of the set-in sleeve, then pull the tape down until you reach the sleeve hem.