Fat Man
USA · 1945 · 21 kilotons · pure fission
Overview
Nagasaki bomb.
With a yield of 21 kilotons, the Fat Man is comparable in yield to the Hiroshima bomb. As a pure fission weapon, it derives its energy from nuclear fission of uranium or plutonium.
Fat Man Blast Effects
The table below shows the calculated radius of each effect zone for an air burst (optimal altitude, maximum blast spread) and a surface burst (ground level, with massive radioactive fallout). Formulas are scaling laws from The Effects of Nuclear Weapons (Glasstone & Dolan, 1977).
| Effect zone | Air burst | Surface burst |
|---|---|---|
| Fireball radius | 0.49 km | 0.39 km |
| Severe blast (20 PSI) | 1.32 km | 0.72 km |
| Moderate blast (5 PSI) | 2.81 km | 1.55 km |
| Light blast (1 PSI) | 8.00 km | 4.40 km |
| 3rd-degree thermal burns | 2.33 km | 1.40 km |
| 2nd-degree thermal burns | 4.18 km | 2.51 km |
| Lethal fallout zone | minimal | ~40.6 km |
All values are 1-D ground-distance estimates from the detonation point. Real-world effects depend on terrain, weather, and building construction.
Run the Fat Man on a City
Use the interactive simulator to detonate the Fat Man on any city worldwide. Click any location on the map to see the fireball, blast, and thermal radii overlaid on real geography with population-density-based casualty estimates.
🎯 Simulate Fat ManRelated Weapons
FAQ
How big is the Fat Man blast radius?
In an air burst, the Fat Man produces a fireball roughly 0.49 km in radius and a 5 PSI moderate-blast zone of about 2.81 km — the area in which most residential buildings would collapse. The 1 PSI light-damage radius extends to roughly 8.00 km, where windows shatter.
What is the yield of the Fat Man?
The Fat Man has a yield of 21 kilotons of TNT equivalent. That is comparable in yield to the Hiroshima bomb.
Is the Fat Man bigger than the Hiroshima bomb?
The Hiroshima bomb (Little Boy) had a yield of approximately 15 kilotons. The Fat Man at 21 kilotons is comparable in yield to the Hiroshima bomb.
What thermal burn radius does the Fat Man produce?
Thermal radiation from the Fat Man can cause 3rd-degree burns out to roughly 2.33 km and 2nd-degree burns out to 4.18 km in an air burst. Surface bursts reduce these radii by approximately 40 percent due to ground absorption.