: It took almost 125 years for the human population to increase from 1 billion
: to 2 billion (during the 19th century) - when the population is a third as
: large, the rate of increase is even smaller. 5 years is a pretty short
: timespan - I'd guess we're talking a couple of percent, at best. (If you
: want to consider the fact that humanity is still cleaning up after a
: decades-long war, it's probably even lower than it would be in peacetime -
: it's not like we have nothing to do but sit around and make babies - or
: take care of them.)

: I think using the one hard number we've been given isn't going to steer you
: too far wrong.

You could even use maths:

You have 300 million. in 4 and a half years, you can have 5 cycles of human pregnancy. Let's assume that

- No one died in that period
- Population is equally divided in fertile women and men
- Every cycle produces a single child (so that population increases 150 million every cycle)

5 x 150M + 300M = 1050M

So you have just over a billion humans in human territory, but almost 70% of it is just kids under 5 years-old. As such, 300 million of able-bodies would still be the official count anyway (even of little kids dying is far more dramatic to most people).