Sort products in the table?

How can I sort the products that show up in the table? Or rather, what field are the products being sorted by so I can put order to those?

I have a table of tshirts with the size as a title, and I can't get the table to display the sizes from smallest (Youth Small) to largest (Adult XXL). I've tried altering the title, sku, and weight of the products, and adding the node references one by one and as a group. The order doesn't seem to have anything to do with price or node ID for the individual products.

Thanks in advance for your help!