not sure. i do not understand this sizing chart and cannot find one online either.

I purchased one of these before...I found them to be a bit small. I am 5'9 and weight 163 lbs with an average build/athletic upperbody and the large fits me. I initially bought a medium and had to return. The colors pop out...they are really bright.

click on the picture and keep hitting the arrow until the sizing chart pops up, cuz its there if you know where to look

its by chest diameter and body length

*inches around chest i mean

The rashguard has a pretty snug compression fit. If you're in between sizes, definitely go for the larger of the 2 sizes. I'm 6'1-6'2" and 180 lbs and the Large is pretty snug.
For more specific info, measure the circumference and height of your favorite rashguard and compare to the sizing chart.

Standard rashguard, this model can be worn by both men and women.