Seeing as people were advising to go a size larger, I ended up going for mediums as I'm usually a XS / Small. Ordered Brazil home, USA away and Argentina home; the two Nike kits fit a treat and a normal medium would usually drown me so it was definitely a good move. The Adidas Argie one though is definitely more of a 'real medium', so just a heads up to people to keep your standard size for the Adidas ones but upsize if ordering a Nike shirt.