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Hiroshima nuclear blast radius

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This page loads Little Boy over the Hiroshima hypocenter. The rings are this simulator’s simplified 15 kt airburst. The casualty line uses WorldPop 2020 on today’s grid — not the 1945 population, and not an official fatality total.

Open Hiroshima in the 3D simulator

Educational estimate only. Blast and heat rings use simplified yield scaling. They ignore terrain, weather, shielding, and weapon design. Casualty counts use WorldPop 2020 residents on an approximately 1 km grid and ignore time of day, commuting, shelter, and evacuation. This is not a targeting or civil-defense tool. About the model.

Aim point: 1945 hypocenter (modern downtown) · Weapon: Little Boy (15 kt, 543 m (1,780 ft) optimum airburst)

Ground ranges for Little Boy (15 kt, 543 m (1,780 ft) optimum airburst) in this simulator.
Effect Ground range What the model means
Fireball 266 m (872 ft) Maximum luminous radius
20 psi 839 m (2,751 ft) Heavy destruction
5 psi 1.8 km (1.1 mi) Most buildings collapse
Thermal 2.0 km (1.3 mi) 3rd-degree burns
1 psi 4.2 km (2.6 mi) Windows shatter
Rings scaled to 1 psi. Yellow fireball, red 20 psi, orange 5 psi, gold thermal, blue 1 psi. Not a map of buildings.

Casualty estimate at this pin

People on the WorldPop 2020 grid inside this scenario’s 1 psi ring. Rounded educational estimate, not a forecast.
Estimated deaths 50,005
Estimated injuries 87,506
Residents inside 1 psi 304,709

What the rings cover

The inner rings sit on the downtown hypocenter area. 5 psi covers a large share of the compact central city relative to 1945 Hiroshima’s footprint. 1 psi reaches across much of the basin and still should not be read as a precise wartime damage map.

Little Boy was a uranium gun-type bomb detonated over Hiroshima on 6 August 1945. Open sources place the yield around 15 kt and the burst in the air, not on the surface. This tool uses those round numbers and its own optimum-airburst height, not a surveyed 1945 burst altitude.

The live city is not a time machine. Buildings, parks, and the WorldPop residents are contemporary. Treat this as a scale reconstruction on a real globe, not as a casualty audit of the war.

Nagasaki and the Little Boy weapon page are the natural next reads. Trinity is the test that preceded combat use, with a different device.

Related pages

Nagasaki · Trinity Site · Tokyo · Little Boy

All cities and sites

City index · Historic sites · Weapon yields

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