These sizes are not what they should be. For example, I would recommend 1/12-2 sizes smaller than a regular JC Penny shirt.
Calvin Klein π Herringbone Sleeve Men's Dress Clothing
50 Review
Gildan Performance Men's π Clothing and Shirts with Moisture-Wicking Polyester
44 Review
Men'S Long Sleeve Polo Shirt - Slim Fit, Stretchy, Breathable Collar
43 Review
INFLATION Bamboo Shirts Sleeve Elastic Men's Clothing in Shirts
45 Review