Start here · Nuclear attack
How long to stay
Fallout "uses itself up". The 7-10 rule: each time the time since the blast multiplies by 7, radiation drops by a factor of 10.
Radiation left, compared with hour 1
1 h100%
2 h44%
3 h27%
7 h10%
12 h5.0%
24 h2.0%
2 days1.0%
2 weeks0.10%
25 hours≈ 2.1% of the hour-1 radiation is leftStay inside unless there's immediate danger or an official order. Keep the radio on.
It's an approximation for planning: the real level depends on the weapon, the wind and rain, and only response teams can measure it. More in the 7-10 rule.
