I usually wear a size 8, but the XXL is really tight.
The shirt is really nice quality and I love the design. I wear an 8 in Lululemon shirts and small in 6/small in Oiselle. I originally ordered my De Soto shirt in a large and it was comically small. I returned it and ordered the largest women's size, an XXL, and it's skin tight. I wish the sizing was more inclusive because at my current size I shouldn't be squeezing into an XXL. I know their size guide recommends having the shirt tight for maximum cooling, but I shouldn't have to go up so many sizes and still have the shirt be skin tight.