It starts at 10.49 mb

Im now at 16.14 mb.

Whats yours.

Im roughly at 130 hours

This confused me actually, it was at 10.49mb for the longest time. After pew, maybe 70+ hours it slowly started growing, currently around 13-14mb.

If I remember correctly, they're small compared to Fallout 3 saves.

In a sandbox game like Fallout, a save file has to keep track of so much information. It's not like in, say, an Uncharted game, where a save file need to know the last checkpoint that was hit, what guns are being carried, with how much ammo, and what skin have they got on at the moment! (I'm drilling it down to basics here, I know!)

Fallout 4 has to remember the precise location of every single object you've interacted with (every red ceramic plate, dead corpse, teddy bear, *everything*). Which of the hundreds of lootable containers have got what items in them. Which characters from the dozens of missions have you killed, how much does each companion like you, what are they carrying, and where the heck have they disappeared to now! Locations reset after a set amount of time which helps keep the size down, but it's still a *lot* of data.