The size is measured in centimetres. If you’re American you can check out this version of the map. Made by AplphaDesigner, found on reddit. Disclaimer: Of course size doesn’t matter, don’t worry.
It’s worth noting that while most of the data was from physical measurements by medical personnel, a few are self-reported and it won’t be a surprise to anyone that the latter is the case for France, Italy and Hungary ;) For comparison: Canada 13.9, USA 12.9, Australia 13.3, New Zealand 14.0, Mexico 15.1, Brazil 16.1 and Colombia 17.3.