What If a Nuke Hit San Francisco?

San Francisco has a population of about 826,079 (2025, city proper) and an urban density around 6,798 per km². A Hiroshima-yield warhead (15 kt Little Boy), air-burst at optimum height, would produce a 5 psi moderate-blast radius of about 1.54 km — the zone in which typical homes and lightly built commercial buildings are destroyed. A modern strategic warhead (W76, 90 kt) would extend that moderate-damage zone to roughly 2.80 km, with 3rd-degree thermal burns reaching 4.57 km. Run the interactive simulator above to see the exact zones overlaid on the map.

For a 100 kt strategic warhead air-burst over San Francisco: fireball radius 0.37 km, severe blast (20 psi) 1.02 km, moderate blast (5 psi) 2.80 km, light blast (1 psi) 7.70 km, and 3rd-degree thermal burns 4.57 km. All radii assume an air burst at optimum height and scale with weapon yield.

The 1 psi light-blast radius — roughly the limit of shattered windows and light injuries — runs about 4.26 km for a 15 kt Little Boy versus about 64.1 km for the 50 Mt Tsar Bomba. Blast radius scales roughly with the cube root of yield, so a 3,000× larger weapon extends the radius only about 14×.

This is an educational simulator and does not assess threat probability. San Francisco is one of the world's most prominent cities in North America, which is why we feature it as a scenario. The purpose of these visualizations is to convey the physical scale of nuclear weapons — not to make any operational claim.