I live in the US and wear a Small or Medium dress shirt to work. I had to order XL (US-L) of this particular shirt, because regular L (advertised as US-M) is too tight in the chest, and I'm not a buff guy either. The XL fits me perfectly. These shirts are awesome, but buy a size larger than you normally wear. I'd recommend buying one shirt first to see if it fits, then ordering the rest.

Also, on the plus side, they require no ironing and look perfect!