When ordering our T-Shirts, the best way to decide which size is best for you, is to measure one of your T-shirts. Lay it on a flat surface as shown on the picture and take accurate measurements. Now use the chart below.
If you already know the persons chest size, simply divide that measurement by 2, now find it on the WIDTH column in the chart below.
(40″ chest / 2 equals 20″ this relates to a MEDIUM t-shirt).
All sizes are in inches: