Nuclear bomb blast radius explained
A fireball, a pressure wave, thermal radiation and fallout are different phenomena. A useful blast-radius map states the pressure threshold, yield, burst model and assumptions behind each contour.
What do the 1, 5 and 20 psi rings mean?
Overpressure is pressure above the surrounding atmospheric pressure. The map’s 1, 5 and 20 psi contours are conventional reference thresholds, not lines at which every building has the same outcome. One psi is about 6.9 kPa. Construction, terrain, shielding and blast loading matter.
- 1 psi: a lower-pressure reference; broken glass and other hazards can extend beyond the heavier-damage zones.
- 5 psi: a moderate-blast reference where significant building damage is possible.
- 20 psi: a severe-blast reference, without predicting an individual structure’s response.
These categories summarise scale. They are not a building assessment or a map of safe distances. Glasstone & Dolan, chapter III explains blast propagation and the assumptions behind idealised curves.
Nuclear blast radius examples by yield
The table below is generated from this simulator’s contact surface-burst model in a standard sea-level atmosphere. Distances are radii from the origin, not diameters. Values are rounded model outputs, not observations.
| Yield | Fireball | 20 psi | 5 psi | 1 psi |
|---|---|---|---|---|
| 1 kt | 0.08 km | 0.22 km | 0.44 km | 1.19 km |
| 15 kt | 0.23 km | 0.53 km | 1.09 km | 2.94 km |
| 100 kt | 0.50 km | 1.00 km | 2.05 km | 5.53 km |
| 1,000 kt | 1.26 km | 2.16 km | 4.42 km | 11.91 km |
The 15 kt row is an energy-scale comparison. It does not reconstruct Hiroshima, which was an airburst. Read the calculation methods and limitations. You can compare these yields on the interactive map.
How yield changes blast distance
For the same pressure threshold and comparable scaled conditions, blast distance follows approximate cube-root scaling: radius ∝ yield1/3. Raising yield from 100 kt to 800 kt doubles the reference blast radius. It does not imply uniform damage inside the enlarged circle. This scaling is described in Glasstone & Dolan §3.61.
Surface burst versus airburst
A surface burst interacts with the ground. An airburst’s incident and reflected shock waves interact differently, so its pressure contours cannot be obtained merely by lifting a surface-burst circle into the air.
This tool uses a surface curve fit or a separate reflected-airblast fit for one fixed, scaled airburst reference height. It does not search for an optimal height. At 100 kt, those two reference scenarios give approximately 2.05 km and 2.97 km respectively for 5 psi; changing the burst geometry changes the result.
Why the thermal and fallout layers differ
The thermal layer is a simplified radiant-energy budget, not a burn-distance prediction. The fallout layer is an optional idealised surface-burst pattern shaped by a single effective wind. Neither is another blast-pressure ring. Learn how to read a nuclear fallout map.
Blast-radius questions
Does a nuclear bomb have one blast radius?
No. A blast-radius map normally draws separate pressure thresholds. Fireball size, radiant heat and fallout are different effects, with different ranges and assumptions.
Does eight times the yield mean eight times the radius?
At a fixed pressure and comparable scaled burst conditions, blast radius scales approximately with the cube root of yield. Eight times the yield gives about twice the radius and four times the circular area, not eight times the radius.
Can the simulator reproduce Hiroshima or Tsar Bomba?
Historical yield labels are energy comparisons, not reconstructions of particular events. This version supports 1 to 10,000 kt. The supplied 50 Mt Tsar Bomba test entry is reference-only because it exceeds that range.
Sources and scope
Glasstone & Dolan (1977), chapter III, including §3.61; CEX-62.2 surface-burst fit, equation 2.5; and Brode (1986), as implemented by GOFAI/glasstone (MIT) for the fixed airburst. See the methodology for attribution and exclusions.