# How do I calculate rough fireball/blast radius for nuke explosions?

As some of us know, PBS’ old “blast mapper” page is now effectively defunct, for various reasons. And by that I mean that it won’t let one plug in the exact map location for the blast-map to be superimposed over. Truly, a sad day for all of us who enjoyed “dropping” a 25-MT nuke on our own houses.

But…surely there’s some mathematical formula for calculating fireball. crater, and blast radius, based on explosive tonnage?

Of course, any perfect calculations of a nuclear blast’s effects would have to take into account complex variables like detonation altitude, local terrain, atmospheric conditions, etc. But I wouldn’t need an exact calculation, just the rough “ballpark” estimate. Probably assuming the blast is a surface detonation.

I don’t suppose it’d be anything so simple as " (y) kilotons of explosive power divided by 3.14 = (y) crater diameter in feet"?

This site calculates the fireball based on the number of megatons entered.

I think the ground crater would depend on the altitude of the nuke at the time it detonates.

I don’t know of any online substitutes, but the standard work is The Effects of Nuclear Weapons (various editions) by Glasstone and Dolan, the essential reference for any Cold Warrior with a city to nuke. They summarise what’s known about the physics of the different effects. In some cases these can be expressed as relatively simple formulae, but in other cases they tabulated and graphed what was learnt from the US bomb tests.

Famously, it comes with a circular plastic “Nuclear Bomb Effects Computer” tucked into a pocket inside the back cover. This allows you to conveniently “dial-up” a yield and read off things like crater size or the physical and biological effects at different distances. Hours of fun when you’re in an apocalyptic mood.

Thanks! Y’all just made my weekend…

Woah, I just checked the figures for 1000 gigaton explosions, and I sure hope that antimatter weapons never get used.

I seem to recall that the primary blast radius (the crater, for a ground burst) is supposed to be 20 feet per caster level. Does that apply to nuclear weapons?

No, Scuba_Ben, a nuclear explosion is considered to be the equivalent of the 9th-level spell apocalypse from the sky from the Book of Vile Darkness. It has a blast radius of 10 miles per caster level, which means a minimum of 170 miles. Of course, the caster is almost certain to be vaporized as well, but when you’re a psychopathic evil archmage, that’s considered a bonus.