I'm 5ft 9in and about 170lbs. In a tailored suit or jacket, I would be 40R. This puts me right on the borderline between M and L when it comes to t-shirt sizes. Some of the larger sizes may be too big for me, but this one fits perfectly. A medium size would be too small. These shirts are also of good quality.
Ultimate Comfort and Style: Minus33 Merino Wool Ticonderoga Lightweight Men's Clothing, T-Shirts & Tanks
43 Review
Ultimate Comfort: Discover the Comfort Colors Sleeve 6014 - X Large Men's Clothing, T-Shirts & Tanks
40 Review
Ashers Apparel Schrute Breakfast T Shirt Men's Clothing for T-Shirts & Tanks
34 Review
Next Level Premium Fitted N6210: High-Quality Men's Clothing & Essential T-Shirts + Tanks Collection
39 Review