Fat Man on New York
21 kt fission weapon · USA · Population 8,336,817 · Density 10,000/km²
About this scenario
This page calculates what would happen if the Fat Man (USA, 1945) detonated over New York (USA). Nagasaki bomb.
The most populous city in the United States and a global financial capital, with a metropolitan area approaching 20 million people. With an urban-core density of about 10,000 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 New York)
| Effect zone | Radius | Est. affected |
|---|---|---|
| Fireball (vaporization, 100% fatal) | 0.49 km | ~7,545 |
| Severe blast (20 PSI, ~98% fatal) | 1.32 km | ~45,805 |
| Moderate blast (5 PSI, ~50% fatal) | 2.81 km | ~97,078 |
| Light blast (1 PSI, glass injuries) | 8.00 km | ~88,152 |
| 3rd-degree thermal burns | 2.33 km | — |
| 2nd-degree thermal burns | 4.18 km | — |
Estimated total fatalities: ~150,428 · Estimated total affected (inside 1 PSI light-blast radius): ~2,011,638.
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 New York.
| 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 New York 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 New York?
In an air burst over New York, 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 New York's urban density (~10,000/km²), this scenario yields an estimated 150,428 immediate fatalities and about 88,152 additional injured.
How many people would die in New York from a Fat Man strike?
An air burst of the Fat Man over New York could cause an estimated 150,428 immediate fatalities and 88,152 additional injuries. The fireball alone (radius 0.49 km) would kill approximately 7,545 people; the severe-blast zone (20 PSI, radius 1.32 km) would add 45,805; the moderate-blast zone (5 PSI, radius 2.81 km) would add 97,078 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 New York?
For an air burst over New York: 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.