Fat Man vs Trinity
Nuclear weapon side-by-side comparison
Fat Man
USA · 1945 · pure fission
21 kt
Nagasaki bomb.
Trinity
USA · 1945 · pure fission
25 kt
First nuclear test.
Verdict
The Trinity is 1.2× more powerful than the Fat Man by yield. Both weapons are described in detail below, with side-by-side blast and thermal radii, casualty estimates at a reference urban density, and historical context.
Blast & thermal effects (air burst)
| Effect zone | Fat Man | Trinity |
|---|---|---|
| Yield | 21 kt | 25 kt |
| Fireball radius | 0.49 km | 0.53 km |
| Severe blast (20 PSI) | 1.32 km | 1.39 km |
| Moderate blast (5 PSI) | 2.81 km | 2.98 km |
| Light blast (1 PSI) | 8.00 km | 8.48 km |
| 3rd-degree thermal burns | 2.33 km | 2.51 km |
| 2nd-degree thermal burns | 4.18 km | 4.49 km |
Casualty estimate (dense urban target)
Estimated immediate fatalities if each weapon air-bursts over a city center with a population density of about 8,000 per km² (representative of dense urban cores like Manhattan or central Paris):
Real casualties depend strongly on time of day, sheltering, weather, and altitude of detonation. See the methodology page for the underlying formulas.
Hiroshima reference
The Hiroshima bomb (Little Boy) had a yield of approximately 15 kilotons. The Fat Man is 1× more powerful than the Hiroshima bomb. The Trinity is 2× more powerful.
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FAQ
Is the Fat Man bigger than the Trinity?
No. The Trinity (25 kt) is 1.2× more powerful than the Fat Man (21 kt).
What is the blast radius of the Fat Man compared to the Trinity?
For an air burst, the Fat Man produces a 5 PSI moderate-blast radius of 2.81 km, versus 2.98 km for the Trinity. Severe blast (20 PSI): 1.32 km vs 1.39 km. 3rd-degree thermal burns: 2.33 km vs 2.51 km.
How many people would die from a Fat Man compared to a Trinity?
Detonated over a typical dense city center (8,000 people/km²), the Fat Man would cause an estimated 120,341 immediate fatalities. The Trinity would cause an estimated 135,018. Real numbers depend on time of day, sheltering, weather, and altitude of detonation.
How do the Fat Man and Trinity compare to the Hiroshima bomb?
The Fat Man is 1× more powerful than the Hiroshima bomb (Little Boy, 15 kt). The Trinity is 2× more powerful than the Hiroshima bomb.