La Stabilite Ferrari T-shirt 

Body Length, Take from the top of the shoulder, close to the mid side of your neck, following your body down to the point where you want your shirt to end. Think of a line going from your armpit straight upwards to your shoulder. Measure between those two points and hold the tape measure straight.

Chest Width, Take a tape measure and wrap it under your armpits at the fullest part of your chest. Stand straight and don't puff out your chest. Keep the tape measure taut, but not constricting. It shouldn't be squeezing down your chest.