I mostly read the reviews about the size. I usually order a large shirt. With this material I tried it this time with a medium. My chest measurement is 39 inches. Fit is perfect! I wore it one day sea fishing off Anna Maria Island in Florida. The temperature was 88 degrees. I was comfortably cool and although my face got too much sun because I forgot to put sunscreen on, everything else from my head to my waist was protected from the sun! And yes, I'm a ginger! Good product!