A couple of publications have revealed the map size.
It’s started happening, guys! Fallout 4 leaks are showing up on the internet aplenty, and if you don’t want any information on the game, if you just want to go in blind, then it’s best to just not read anything about Fallout 4 for the next few days- including this news piece. This is your final chance to leave, because after this, there may be spoilers.
Anyway, GameRevolution posted an image of the in game map, stitched together from disparate screenshots, which apparently shows us what the full game world looks like. It seems to be pretty big, with quite a bit of water, although bizarrely, GameRevolution estimates the game world size to be just 145,800 square feet. A much more accurate estimate of the map size comes from Eggplante, who estimate it to be between 400 million square feet (14.3 square miles) and 1.2 billion square feet (43 square miles).
Fallout 4 launches next week on Xbox One, PlayStation 4, and PC. Stay tuned.