What if a Nuclear Bomb Hit San Francisco?
USA · Population 873,000 · Density 7,300/km²
About San Francisco
The financial and technology capital of the western United States, on a dense 121 km² peninsula.
Below are four scenario calculations using historical and modern nuclear weapons. Each row shows the radius of an effect zone in kilometers and a rough order-of-magnitude estimate of people inside that zone, derived from the city's urban population density. Numbers are educational approximations — see the methodology page for the underlying formulas.
Little Boy on San Francisco (15 kt)
USA · 1945 · Hiroshima bomb
| Effect zone | Radius | Est. affected |
|---|---|---|
| Fireball (vaporization, 100% fatal) | 0.43 km | ~4,208 |
| Severe blast (20 PSI, ~98% fatal) | 1.18 km | ~26,982 |
| Moderate blast (5 PSI, ~50% fatal) | 2.52 km | ~56,754 |
| Light blast (1 PSI, glass injuries) | 7.16 km | ~51,536 |
| 3rd-degree thermal burns | 2.03 km | — |
W76 on San Francisco (100 kt)
USA · 1978 · Common SLBM warhead
| Effect zone | Radius | Est. affected |
|---|---|---|
| Fireball (vaporization, 100% fatal) | 0.91 km | ~19,196 |
| Severe blast (20 PSI, ~98% fatal) | 2.20 km | ~89,896 |
| Moderate blast (5 PSI, ~50% fatal) | 4.71 km | ~198,507 |
| Light blast (1 PSI, glass injuries) | 13.39 km | ~180,256 |
| 3rd-degree thermal burns | 4.43 km | — |
Castle Bravo on San Francisco (15 Mt)
USA · 1954 · Most powerful US nuclear test
| Effect zone | Radius | Est. affected |
|---|---|---|
| Fireball (vaporization, 100% fatal) | 6.79 km | ~1,057,016 |
| Severe blast (20 PSI, ~98% fatal) | 11.51 km | ~1,921,590 |
| Moderate blast (5 PSI, ~50% fatal) | 24.60 km | ~5,419,951 |
| Light blast (1 PSI, glass injuries) | 69.98 km | ~4,921,661 |
| 3rd-degree thermal burns | 34.54 km | — |
Tsar Bomba on San Francisco (50 Mt)
USSR · 1961 · Largest nuclear weapon ever tested
| Effect zone | Radius | Est. affected |
|---|---|---|
| Fireball (vaporization, 100% fatal) | 10.99 km | ~2,769,394 |
| Severe blast (20 PSI, ~98% fatal) | 17.13 km | ~3,824,062 |
| Moderate blast (5 PSI, ~50% fatal) | 36.60 km | ~11,997,625 |
| Light blast (1 PSI, glass injuries) | 104.12 km | ~10,894,611 |
| 3rd-degree thermal burns | 56.58 km | — |
Limitations
These estimates assume an idealized air burst over the city center, uniform population density, and no advance warning or sheltering. Real-world casualties would depend on:
- Time of day (population is concentrated downtown during business hours)
- Sheltering and basements (subway systems can reduce casualties significantly)
- Building construction (reinforced steel/concrete vs. wood-frame)
- Weather and atmospheric conditions
- Detonation altitude (air burst vs. surface burst)
- Subsequent fallout and infrastructure collapse
Other City Scenarios
FAQ
What would happen if a nuclear bomb hit San Francisco?
San Francisco has approximately 873,000 people and an urban density around 7,300 per km². A Hiroshima-yield warhead (15 kt Little Boy) detonated over San Francisco would produce a moderate blast radius of about 2.5 km, with an estimated 31,190 immediate fatalities in the severe-blast zone. A modern strategic warhead (W76, 100 kt) would extend the moderate-damage zone to roughly 4.7 km with thermal burns reaching 4.4 km. Run the interactive simulator above to see the exact zones overlaid on the map.
How many people would die in San Francisco from a nuclear strike?
A 100 kt W76 strategic warhead air-burst over San Francisco could cause an estimated 307,599 immediate fatalities and around 180,256 additional injured. For comparison, a 50 Mt Tsar Bomba — the largest weapon ever tested — would put roughly 248,615,486 people inside the 1 PSI light-blast zone alone. Real casualties depend strongly on time of day, sheltering, weather, and altitude of detonation.
What is the blast radius of a nuclear bomb over San Francisco?
For a 100 kt strategic warhead over San Francisco: fireball radius 0.91 km, severe blast (20 PSI) 2.20 km, moderate blast (5 PSI) 4.71 km, light blast (1 PSI) 13.39 km, third-degree thermal burns 4.43 km. Larger yields scale these radii roughly as the cube root of yield for blast and the 0.41 power for thermal effects.
Is San Francisco a likely nuclear target?
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 humanitarian scale of nuclear weapons — not to make any operational claim.