I just got my shirt yesterday. I'm so bummed. I ordered the size recommended by the chart, a women's xl, and worried that it would be too small, given that the site says to size up.
I could probably wear a medium. Of course, there are no returns. Women, if this is your first shirt, be careful. To give some perspective, I wear an xl or a 2xl in other women's shirts. I held this up to my husband's men's large shirts (most are from kohl's), and it was a touch bigger.
Do NOT follow their advice to size up. I'm just hoping they shrink massively.