Castle Bravo vs Little Boy
Nuclear weapon side-by-side comparison
Castle Bravo
USA · 1954 · thermonuclear
15 Mt
Most powerful US nuclear test.
Little Boy
USA · 1945 · pure fission
15 kt
Hiroshima bomb.
Verdict
The Castle Bravo is 1,000× more powerful than the Little Boy 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 | Castle Bravo | Little Boy |
|---|---|---|
| Yield | 15 Mt | 15 kt |
| Fireball radius | 6.79 km | 0.43 km |
| Severe blast (20 PSI) | 11.51 km | 1.18 km |
| Moderate blast (5 PSI) | 24.60 km | 2.52 km |
| Light blast (1 PSI) | 69.98 km | 7.16 km |
| 3rd-degree thermal burns | 34.54 km | 2.03 km |
| 2nd-degree thermal burns | 61.86 km | 3.64 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 Castle Bravo is 1,000× more powerful than the Hiroshima bomb. The Little Boy is 1× more powerful.
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FAQ
Is the Castle Bravo bigger than the Little Boy?
Yes. The Castle Bravo (15 Mt) is 1,000× more powerful than the Little Boy (15 kt).
What is the blast radius of the Castle Bravo compared to the Little Boy?
For an air burst, the Castle Bravo produces a 5 PSI moderate-blast radius of 24.60 km, versus 2.52 km for the Little Boy. Severe blast (20 PSI): 11.51 km vs 1.18 km. 3rd-degree thermal burns: 34.54 km vs 2.03 km.
How many people would die from a Castle Bravo compared to a Little Boy?
Detonated over a typical dense city center (8,000 people/km²), the Castle Bravo would cause an estimated 9,203,897 immediate fatalities. The Little Boy would cause an estimated 96,377. Real numbers depend on time of day, sheltering, weather, and altitude of detonation.
How do the Castle Bravo and Little Boy compare to the Hiroshima bomb?
The Castle Bravo is 1,000× more powerful than the Hiroshima bomb (Little Boy, 15 kt). The Little Boy is 1× more powerful than the Hiroshima bomb.