ad 4 In the US, I wear a medium. But I went for an XL this time. The fit and cut are good. I have an athletic build. The length is long enough to stay tucked in. Nice details with the buttons. The layered look at the collar and sleeves is nice too. The material is a bit thin, but I wear white undershirts, so not a big deal. I bought 2 white ones, but will probably buy 1 more white, and maybe a few other colors. Recommended.