Little Boy (Hiroshima Bomb) Blast Radius

Little Boy, the bomb dropped on Hiroshima, was about 10 feet long and 28 inches in diameter. Published weights range from 8,900 lb (Sublette) to about 9,000 lb (US Air Force museum) and 9,700 lb (National Museum of Nuclear Science & History). It was a gun-type uranium weapon with a yield of 15 kilotons.^{[5, 6, 1]}

The Hiroshima bomb had a yield of 15 kilotons, or 15,000 tons of TNT equivalent, according to the US government test catalogue DOE/NV-209. In an air burst at optimum height that is enough to collapse most houses to a radius of roughly two kilometres and to shatter windows several kilometres further out.^[1]

For a 15-kiloton air burst the simulator computes a fireball radius of about 0.18 km, a 5 psi moderate-blast radius of about 1.5 km (the level at which most houses would collapse) and a 1 psi light-damage radius of about 4.3 km, where windows break. Thermal radiation reaches third-degree-burn range at about 2.2 km.^{[3, 4]}

Fifteen kilotons, which is 15,000 tons of TNT equivalent (DOE/NV-209). The 1945 White House announcement spoke of "more power than 20,000 tons of TNT," a wartime estimate; the measured figure settled at 15 kt.^{[1, 8]}

In an air burst at optimum height, the Little Boy produces a fireball roughly 0.18 km in radius and a 5 psi moderate-blast zone of about 1.54 km — the area in which most residential buildings would collapse. The 1 psi light-damage radius extends to roughly 4.26 km, where windows shatter.

In an air burst at optimum height, thermal radiation from the Little Boy can cause 3rd-degree burns out to roughly 2.18 km, 2nd-degree burns to 2.80 km, and 1st-degree burns to 3.69 km.