After reading several reviews I was able to choose the right size for me. I usually wear XL and XXL because I have 21" biceps, 43" chest and broad shoulders. So I bought XXXL as several reviews mentioned that the shirts run very small. As expected it is tight around my arms but not so tight to wear I would be uncomfortable. I assume it will sit and it will fit perfectly. This is a very light fabric and ideal for those who want to run in 45 degree weather in winter. You need to increase your cardio.