CD Projekt Red and Umbra Software held a presentation titled "Solving Visibility and Streaming in The Witcher 3: Wild Hunt with Umbra 3" at the Game Developers Conference, and it included a very interesting detail (that I happened to overlook when I first examined the original slides) as discovered by Reddit user fughp.

The slides mention the size of two of the areas included in the game: the city of Novigrad measures 8.5 x 8.5 km for a total size of 72,25 square km, while Skellige is 8 x 8 km, meaning 64 square km. Summed up, the two areas cover 136,25 square km, which convert to just north of 52 square miles.

By comparison, The Elder Scrolls V: Skyrim's world has been calculated to measure 14.8 square miles. This means that the two areas named above are already over 3.5 times larger than the whole Skyrim map.

This is actually fairly interesting since back in June CD Projekt RED described The Witcher 3 as 20% larger than Bethesda's open world game. We currently don't know if that was just a preliminary estimate, or the Witcher's world just got bigger since then.

We reached out to CD Projekt RED requesting information to shed light on the issue, and we'll keep you updated if we receive any relevant answer. In the meanwhile one thing is for sure: the world of The Witcher 3: Wild Hunt is pretty damn big.