Microsoft has revealed the file size for Fallout 4 over at Xbox.xom. It turns out the game size only is 28.12 gigabyte(PC and PlayStation 4 are typically similar), and while that is way bigger than any previous Bethesda game, it's still almost half the size of the upcoming Halo 5: Guardians (46.19 gigabyte).
It's worth noting that a day 1 patch of several gigabytes is likely to be required when Fallout 4 launches on PC, PlayStation 4 and Xbox One on November 10th.
Thanks, Gamespot.