So I've always been curious about how big vaults are in the FO games. You always see Doors you can't go thru etc. And in FO3 the LW comments [Though could of been sarcastic] "The "Outdoor" area is huge, you can't even see the ceiling". So has it ever been said how big vaults are and what kind of area's each contains? Or is it what you see in the games, various corridors and small rooms?

To have a viable breeding population (as these were supposed to be Arks that just don't go anywhere) you need 500 to 1000 people. Even then, strict controls are needed to stop the effects of inbreeding over time. Given that they probably expected to be down for 200 years, the Viable Population could be smaller for a shorter period of time, So, I would imagine the vaults would need to house, feed and care for 200 to 1000 people, or it just would not be worth it.

Of course we know that Vault-Tec was not the most altruistic of companies, so they probably had populations of varying sizes to fit their experiments, not the continuity of the human race.

Vaults, these days anyway, don't have a standard design (they used to it appeared). But it depends entirely on the Vault and what-ever it's ulterior motive was - Vault 112 is relatively small for example.

In Fallout 1 and 2 Vaults used a hot-bunking system, people didn't have personal apartments, which I imagine would reduce space considerably.

I think lore-wise the vaults would have to be bigger than we see in game(in FO3 and FONV at least, haven't played FO or FO2). It's safe to assume that they suffered in scope just like most towns did due to console performance and limited development resources.

Depends on the Vault, I believe Vault 13 had a thousand people.

They're underexaggerated in the game, for obvious reasons. To have enough space for 1000 people (and then god knows how many they multiply) it would have to be very very large.

Considering Vaults 68 and 69.... definitely not concerned with the survival of the human race

I wonder how big Vault 77 was also... I should hope it was just a miniature sized one, otherwise what a waste of space...