Nuclear Blast Radius Calculator

What a blast radius means

A nuclear explosion does not have one edge. It produces a set of nested effects, each reaching a different distance, so a bomb has not one radius but several. The useful way to read “blast radius” is as a set of rings: the fireball, three levels of blast pressure, and three levels of heat burn.

When a single number is quoted, it is almost always the 5 psi overpressure radius, the distance within which most ordinary houses collapse. On this page the calculator and the chart below give you all seven rings at once, in miles first and kilometers in parentheses, so you never have to guess which one a headline meant.

Nuclear blast radius chart: 1 kt to 50 Mt

Every radius here is produced by the same engine as the calculator and the map, for an air burst at optimum height. Each number is calculated from scaling laws, not measured. Named rows link to the full weapon profile.^{[1, 2]}

Fireball: Glasstone & Dolan 1977 §2.127. Blast and thermal: the standard scaling-law table (optimum-height air bursts). Values in mi (km); swipe sideways on a phone to see every ring.^{[1, 2]}

Worked example: a 1-megaton air burst

Take a 1-megaton bomb, roughly the size of the B83, the largest weapon still in the US stockpile. Detonated as an air burst, it produces these seven rings, closest to farthest:

The fireball (0.6 mi (0.97 km)) vaporizes anything inside it, but it is the smallest ring. The 20 psi ring (1.5 mi (2.4 km)) destroys even heavy concrete buildings; the 5 psi ring (3.9 mi (6.2 km)) collapses most houses — this is the number most people mean by “blast radius.”

Lighter blast reaches much farther: 1 psi (11 mi (17 km)) shatters windows. And the heat flash burns exposed skin to the edge of the map: first-degree burns out to 12 mi (19 km), farther than the 5 psi blast.

How to read your results

Each ring answers a different question. From the center outward:

Fireball

The sphere of plasma at the detonation point. Anything inside is vaporized. It is the smallest radius and sets the scale for the rest.

20 psi (severe blast)

The pressure that collapses reinforced-concrete buildings. Survival is near zero inside this ring.^[3]

5 psi (moderate blast)

The headline “blast radius.” Most houses collapse and fires start.

1 psi (light blast)

Windows shatter across a wide area; flying glass is the main injury. It covers by far the largest area of the blast rings.

3rd / 2nd / 1st-degree burns

How far the heat flash can burn exposed skin, from severe (3rd) to sunburn-like (1st). These assume clear weather and a direct line of sight to the fireball.

The fireball

The fireball is the sphere of superheated gas at the center of the explosion. For a split second it reaches tens of millions of degrees, as hot as the center of the Sun.^[4] Everything inside it is vaporized.

It is also the smallest ring, and it grows slowly: fireball radius scales with yield to the 0.4 power. A 15-kiloton bomb makes a 0.11 mi (0.18 km) fireball; a 1,000-times-larger 15-megaton bomb makes one of only 1.8 mi (2.9 km). The destruction you picture comes from the blast wave and the heat, not from the fireball touching you.

Overpressure and psi

Overpressure is the pressure of the blast wave above normal air pressure, measured in pounds per square inch. It is how blast damage is graded: 20 psi destroys reinforced concrete, 5 psi collapses most homes, and 1 psi breaks windows.^[3]

Psi (pounds per square inch) is just the unit of that pressure. A few psi sounds small, but a 5 psi wall of air moving at highway speed is what flattens a neighborhood. Overpressure radius grows with roughly the cube root of yield, which is why the rings widen so slowly as bombs get bigger.^[5]

Thermal radiation and burns

Thermal radiation is the flash of light and infrared heat that leaves the fireball at the speed of light. Because it travels in straight lines, it burns any exposed skin with a clear view of the fireball, often farther than the blast wave reaches.

Burns are graded by depth. Second-degree burns blister the skin; third-degree burns destroy it; first-degree burns are like sunburn. For a 1-megaton air burst, second-degree burns reach 9.3 mi (15 km) and first-degree burns 12 mi (19 km). These ranges assume clear weather; haze, cloud or terrain shorten them.^{[1, 2]}

Air burst vs surface burst

An air burst detonates the weapon above the ground, at the height that maximizes the area covered by a chosen blast pressure. Hiroshima and Nagasaki were both air bursts. It produces the widest blast and thermal rings and very little local fallout. Every number on this page assumes an air burst at optimum height, because that is the case the engine models.

A surface burst detonates at ground level. For most overpressures its blast reaches less far than an optimum-height air burst, but it digs a crater and throws up heavy radioactive fallout that drifts downwind. Surface-burst radii are not shown here: the scaling the site uses is verified for air bursts only, and unverified effects are withheld rather than guessed.

How the radius grows with yield

Blast radius grows with roughly the cube root of yield, so each extra ton of explosive buys less reach than the last. A 1,000-fold jump in yield (from 1 kiloton to 1 megaton) widens the 5 psi ring only about tenfold, from 0.37 mi (0.6 km) to 3.9 mi (6.2 km).^[5] The chart shows that flattening across the whole database.

How far a nuke reaches

“How far does a nuke reach?” has three answers, because blast, heat and fallout travel differently. Blast reaches the 1 psi window-breaking line, 11 mi (17 km) for a 1-megaton air burst. Heat can reach farther: first-degree burns extend to 12 mi (19 km) at 1 megaton, and to 45 mi (73 km) for the 50-megaton Tsar Bomba — past even its 1 psi blast (40 mi (64 km)).^{[1, 2]}

Fallout can travel hundreds of miles downwind, far beyond any blast or heat ring, but only from a surface burst and only in a pattern set by the wind. Because that depends on weather, it is not part of these radii; see the fallout definition for how it behaves.

Nuclear missile blast radius

People searching for a “nuclear missile blast radius” usually picture a Tsar-Bomba-sized blast. Real deployed warheads are far smaller: most sit in the 100-to-500-kiloton range to pack several onto one missile. Here is the 5 psi radius for the warheads in the database:^{[1, 2]}

• W76 (90 kt): 5 psi radius 1.7 mi (2.8 km)
• W87 (300 kt): 5 psi radius 2.6 mi (4.2 km)
• W88 (455 kt): 5 psi radius 3 mi (4.8 km)
• B61 (340 kt): 5 psi radius 2.7 mi (4.3 km)
• B83 (1.2 Mt): 5 psi radius 4.1 mi (6.6 km)

A single ICBM often carries several of these on independent warheads, so the real question is less about one blast radius than about many at once. See the arsenals by country for how many each nation fields.

Ways to use this

Frequently asked questions

Methodology and sources

Fireball radius uses the Glasstone & Dolan 1977 relation (§2.127); blast and thermal radii come from the standard scaling-law table for optimum-height air bursts, interpolated on a log-log scale. Every figure on this page, in the calculator, the chart and the diagrams, is produced by that one engine, the same one behind the map. Full working: methodology.

What is not shown: casualty counts, fallout, radiation dose and surface-burst effects are withheld until each has a verified model. Radii are 1-D ground-distance estimates; real effects depend on terrain, weather and construction. Do not use them for emergency planning.

Data as of 22 October 2026. By Marko Visic, BSc Physics.