Whites Boot's Sizing Information

White's Boots are an American boot brand that uses US Sizing. However they are built on heritage lasts so they're sizing is one size bigger. This is also true of other heritage boot brands.

You should purchase the same size White's Boots that you would wear in Red Wing Boots, Wesco Boots etc.

You should purchase ONE SIZE DOWN from your typical US Sneaker size.
This size happens to be your UK Size. 

Example : if you wear a US Size 10 in Nike, Vans etc you should purchase a US Size 9 in White's Boots. If you are a UK9 in Dr Marten's or Converse (which uses UK sizing) you should buy the same size.