They come in various sizes. there should be a drop down box to choose a size.
If you are not seeing a drop down box, you might want to Email "orders@ironmaglabs.com" and ask them prior to purchase.
I own several of these and they are beyond comfortable shirts. These by far are my favorite material I have ever owned.
You can use discount codes on accessories like shirts as well, so feel free to use my code "WES15" if and when you order!!