I bought three of these in XL, neon pink, neon blue, and royal.  The two neons are a cotton/poly blend, the royal is all cotton.  I'm a size 12 and wear an L in tops unless I want it loose fitting or it looks like it will shrink.  All 3 seemed on the large side before washing, especially the pink.  After washing they royal was perfect, the neon blue was a good fit but the pink was still large.  I tacked up the shoulders a bit and it's wearable for my purpose, something comfortable for walking or exercise videos.  Based on these three I'd say if you're a size L, don't go up.  If you're between sizes don't go up on the pink, and you probably don't have to on the royal and neon blue.  Btw, these washed up very nicely, there was no twisting in the fabric and the colors didn't run.  They are a very soft, supple cotton and to the touch, I can't tell the blend from the pure cotton. I'll buy these again without hesitation.