I'd always heard good things about Under Armour products, so decided to give the HeatGear longsleeve T a try.  I went by the sizing chart on the Amazon website under Product Description.  My measurements fit a size Small perfectly.  I typically wear a small top and a size 2 pant.  I was shocked when my T-shirt arrived to discover that it was so small I couldn't even pull it over my head and shoulders to try it on.  By the looks of this T-shirt, I'd have to have at least a Large to be able to get it on. I know it's supposed to fit snugly, but this was ridiculous.