According to this wiki entry radiation has the following effect:

The rate is 1% of HP per 10 rads;

But what does +2 RADS (as an example, see on the screenshot) stand for? Does it mean, that you get +2 RADS every second and so you would die after (10/2)*100 sec? (Example provides that the radiation doesn't change in this time and that you are full-life in the beginning of this experiment.)

I haven't found anything about units regarding this topic.

radiation +2 screenshot

  • My guess is that when it comes up after eating/drinking something it is an absolute measure, aka you gain exactly the rads it says, and if it shows up from ambient radiation like sitting around in the water it means rads per second. – leinaD_natipaC Dec 1 '15 at 15:09
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    @leinaD_natipaC that's right. Eating moldy food, for example, states that it gives you 6 rads. In effect, it basically displays the +6 rads indicator, and gives you +6 rads for a 1 second duration. – king14nyr Dec 1 '15 at 15:20
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    I don't quite understand the title of the post... The "unit" is clearly Rad, yet the question seems to be asking how this value affects health over time. Unless I'm misunderstanding the title? – Broots Waymb Dec 1 '15 at 16:50
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    @h0ch5tr4355, really? I'm pretty sure it's real... en.wikipedia.org/wiki/Rad_%28unit%29 but yes, the "per second" clarification makes sense. – Broots Waymb Dec 1 '15 at 16:57
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    @h0ch5tr4355 Rad is not a fictive unit – IllusiveBrian Dec 1 '15 at 16:58

The rate is 1% of HP per 10 rads, meaning you lose 1% of your max health per 10 radiation you take. This is indicated by the red bar that grows from the right side of your health bar when you incur radiation. If your 100 health max character takes 200 radiation, your max health is now 80 until you lower your radiation.

Using this formula, and confirmed by the max value on the "radiation" indicator on the right side of the Pip-Boy, 1000 radiation is lethal. 1000 radiation would reduce your max hp by 100%.

When you are receiving radiation, you'll get the indicator by your health bar. +2 rads would indicate you are taking 2 radiation per second. The time it would take to kill you while receiving x rads per second would be: (1000 - CurrentRadiationLevel)/x seconds.

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    Probably not so coincidentally, 1000 rads is considered a lethal dose in real life also. – tpg2114 Dec 1 '15 at 15:47
  • That's some useful information, and specific enough that I imagine it's true. I don't see any testing in this answer, where did you get the information? – DCShannon Dec 1 '15 at 19:17
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    @DCShannon Some from my own experience testing with rads/resistances while just sitting in the Cambridge Crater. Most is from the Fallout Wiki Page on Radiation, which has a bunch of great info on rad accumulation, affects, and even intricacies on how the radiation weapons work with radiation resistances/immunities. – king14nyr Dec 1 '15 at 20:26

The lethal radiation dose is same as in previous games 1000 rads. So you will be dead after 500 seconds of exposure too +2 rads a second.


If I remember correctly, then on the pipboy in Fallout 3, you have a radiation meter in the Stats section, which maxed out at 1000. Thus, a lethal dose of radiation would be 1000. So, it would take 500 sec of 2 Rads per second to kill you. Likewise, it would take 200 sec of 5 rad per second to kill you, etc.

Also you can eat 200 of something that gives you 5 Rads. And only 100 of things that give you 10 Rads, etc.

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    While it may work in this case, it's not always the best idea to base information about a game off of a previous entry in the series... – Vemonus Mar 30 '17 at 0:55

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