These shirts do NOT run small compared to the Under Armour Heat Gear Compression shirts. In fact all three of these were the same and the forearms were actually larger than the Under Armour sleeves. I don't know what other reviewers were comparing to but if you are familiar with the Under Armour compression shirts these were actually slightly larger. That said, I bought these to protect my skin while push mowing my lawn. I need protection from bugs and sun. I sweat up to 7 Lbs of sweat when I push mow my lawn and cotton shirts are just disgusting after sweating like that. These keep you cooler than bare skin and feel comfortable the whole time.