Named weapon

Fat Man blast radius (21 kt)

Last updated September 13, 2026

Fat Man is a 21 kt airburst preset for the Nagasaki implosion bomb. Trinity uses the same yield as a Gadget analog. The rings are about 10–20% larger than Little Boy’s in this scaling.

Open Fat Man 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.

Yield 21 kt · 607 m (1,991 ft) optimum airburst · Nagasaki, 1945

Ground ranges for Fat Man (21 kt, 607 m (1,991 ft) optimum airburst) in this simulator.
Effect	Ground range	What the model means
Fireball	304 m (998 ft)	Maximum luminous radius
20 psi	938 m (3,078 ft)	Heavy destruction
5 psi	2.0 km (1.3 mi)	Most buildings collapse
Thermal	2.3 km (1.4 mi)	3rd-degree burns
1 psi	4.7 km (2.9 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.

Fat Man was a plutonium implosion weapon. The globe shows a simplified mesh and Glasstone-style radii, not an engineering replica.

Nagasaki’s valley made the real damage pattern irregular. This model still draws circles. Read the Nagasaki page for that caveat, then look at the 3D basin on the globe.

Early Soviet and Chinese first tests sat in this yield class. Semipalatinsk and Lop Nur pages use Fat Man as an analog, labelled as such.

See this yield on a place

Nagasaki · Trinity Site · Semipalatinsk · Tokyo

Other weapons

Little Boy · Fat Man · W76-2 · W76-1 · W87 · W88 · B83 · B53 · Ivy Mike · Castle Bravo · B41 · Tsar Bomba

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