Fat Man on Mexico City
21 kt fission weapon · Mexico · Population 9,209,000 · Density 6,000/km²
About this scenario
This page calculates what would happen if the Fat Man (USA, 1945) detonated over Mexico City (Mexico). Nagasaki bomb.
The capital of Mexico and the largest city in North America by population, with a metro area of over 21 million. With an urban-core density of about 6,000 people per km², even a relatively small detonation over the city center would affect a large population.
The Fat Man delivers 21 kt of explosive yield — comparable in yield to the Hiroshima bomb. The tables below show calculated effect radii for an air burst (optimized for blast spread) and a surface burst (which produces massive fallout).
Air-burst effects (Fat Man over Mexico City)
| Effect zone | Radius | Est. affected |
|---|---|---|
| Fireball (vaporization, 100% fatal) | 0.49 km | ~4,527 |
| Severe blast (20 PSI, ~98% fatal) | 1.32 km | ~27,483 |
| Moderate blast (5 PSI, ~50% fatal) | 2.81 km | ~58,246 |
| Light blast (1 PSI, glass injuries) | 8.00 km | ~52,891 |
| 3rd-degree thermal burns | 2.33 km | — |
| 2nd-degree thermal burns | 4.18 km | — |
Estimated total fatalities: ~90,256 · Estimated total affected (inside 1 PSI light-blast radius): ~1,206,983.
Surface-burst effects (with fallout)
A surface burst trades blast spread for radioactive fallout — much smaller blast radii but a large lethal fallout plume drifting downwind. This is what would happen if the Fat Man struck ground level rather than detonating optimally above Mexico City.
| Effect zone | Radius (surface burst) |
|---|---|
| Fireball | 0.39 km |
| Severe blast (20 PSI) | 0.72 km |
| Moderate blast (5 PSI) | 1.55 km |
| Light blast (1 PSI) | 4.40 km |
| 3rd-degree thermal burns | 1.40 km |
| Lethal fallout zone | ~40.6 km |
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See the actual blast zones overlaid on a map of Mexico City with population-density-based casualty estimates updated in real time as you move the detonation point.
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FAQ
What would happen if the Fat Man detonated over Mexico City?
In an air burst over Mexico City, the Fat Man (21 kt) would produce a fireball about 0.49 km in radius. The 5 PSI moderate-blast zone — where most residential buildings collapse — would extend to 2.81 km. Light blast damage and shattered windows would reach 8.00 km. Given Mexico City's urban density (~6,000/km²), this scenario yields an estimated 90,256 immediate fatalities and about 52,891 additional injured.
How many people would die in Mexico City from a Fat Man strike?
An air burst of the Fat Man over Mexico City could cause an estimated 90,256 immediate fatalities and 52,891 additional injuries. The fireball alone (radius 0.49 km) would kill approximately 4,527 people; the severe-blast zone (20 PSI, radius 1.32 km) would add 27,483; the moderate-blast zone (5 PSI, radius 2.81 km) would add 58,246 more. Real numbers depend heavily on time of day, sheltering, weather, and altitude of detonation.
What is the blast radius of the Fat Man on Mexico City?
For an air burst over Mexico City: fireball 0.49 km, severe blast (20 PSI) 1.32 km, moderate blast (5 PSI) 2.81 km, light blast (1 PSI) 8.00 km. Thermal radiation causes 3rd-degree burns out to 2.33 km. A surface burst would shrink the blast radii by roughly 40 percent but generate massive radioactive fallout extending ~41 km from ground zero.
Is the Fat Man bigger than the bomb that hit Hiroshima?
The Hiroshima bomb (Little Boy) had a yield of about 15 kilotons. The Fat Man at 21 kt is comparable in yield to the Hiroshima bomb.