According to this James Wallis blog post, the World of Warcraft landmass is about the same size as Newcastle.
Newcastle, for those of you that don’t live in the UK, is the main city in the English northeast, notable by the fact people there refuse to wear anything other than t-shirts even when it’s snowing.
“Taken together, the two main continents have a combined area of approximately 113 square kilometres. In terrestrial terms that’s about the same size as the city of Newcastle, or the London Borough of Hillingdon,” said Wallis.
“And if we assume that the world-maps produced by Blizzard Entertainment show approximately the entire surface area of Azeroth then we can wrap it around an imaginary sphere and calculate the diameter of the hypothetical ‘planetoid’ of Azeroth at 12 kilometres.”
More numbers through the link. Thanks RPS.