Little Boy
USA · 1945 · 15 kilotons · pure fission
Overview
Hiroshima bomb.
With a yield of 15 kilotons, the Little Boy is comparable in yield to the Hiroshima bomb. As a pure fission weapon, it derives its energy from nuclear fission of uranium or plutonium.
Little Boy 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 | 0.43 km | 0.34 km |
| Severe blast (20 PSI) | 1.18 km | 0.65 km |
| Moderate blast (5 PSI) | 2.52 km | 1.38 km |
| Light blast (1 PSI) | 7.16 km | 3.94 km |
| 3rd-degree thermal burns | 2.03 km | 1.22 km |
| 2nd-degree thermal burns | 3.64 km | 2.19 km |
| Lethal fallout zone | minimal | ~35.5 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 Little Boy on a City
Use the interactive simulator to detonate the Little Boy 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 Little BoyRelated Weapons
FAQ
How big is the Little Boy blast radius?
In an air burst, the Little Boy produces a fireball roughly 0.43 km in radius and a 5 PSI moderate-blast zone of about 2.52 km — the area in which most residential buildings would collapse. The 1 PSI light-damage radius extends to roughly 7.16 km, where windows shatter.
What is the yield of the Little Boy?
The Little Boy has a yield of 15 kilotons of TNT equivalent. That is comparable in yield to the Hiroshima bomb.
Is the Little Boy bigger than the Hiroshima bomb?
The Hiroshima bomb (Little Boy) had a yield of approximately 15 kilotons. The Little Boy at 15 kilotons is comparable in yield to the Hiroshima bomb.
What thermal burn radius does the Little Boy produce?
Thermal radiation from the Little Boy can cause 3rd-degree burns out to roughly 2.03 km and 2nd-degree burns out to 3.64 km in an air burst. Surface bursts reduce these radii by approximately 40 percent due to ground absorption.