Nuclear Blast Radius Map | See What a Nuke Would Do to Your City

What would happen if a nuclear bomb hit your city?

It depends on two things far more than on anything else: how big the weapon is, and how high above the ground it goes off. Drop a modern 300-kilotonne warhead — the sort carried on an American Minuteman III — on a city centre and the sequence takes about thirty seconds. There is a flash brighter than the sun. A fireball nearly a kilometre wide forms in under a second and everything inside it is vaporised. For roughly two kilometres in every direction, people in the open receive third-degree burns before they have time to look away. Then, several seconds later, the blast wave arrives: reinforced concrete buildings fail out to about 1.4 km, ordinary houses collapse out to 4.5 km, and windows break thirteen kilometres away. Most of the people who die are not killed by the explosion itself but by the buildings falling on them and by the fires that follow.

The simulator above works all of this out for any weapon and any location on Earth. Click a city and watch it happen.

Nuclear blast radius by yield

These are the figures the model above produces for an air burst at the height that does the most damage. Radii scale with the cube root of yield, which is why a weapon a thousand times larger has only ten times the reach.

Yield	Example	Fireball radius	Everything destroyed 20 psi	Houses flattened 5 psi	Third-degree burns	Windows break 1 psi
20 tonnes	Davy Crockett	19 m	56 m	181 m	137 m	541 m
15 kilotonnes	Hiroshima	266 m	512 m	1.6 km	2.0 km	4.9 km
100 kilotonnes	W76, Trident missile	568 m	965 m	3.1 km	4.4 km	9.3 km
300 kilotonnes	W87, Minuteman III	881 m	1.4 km	4.5 km	6.8 km	13 km
800 kilotonnes	Typical large ICBM warhead	1.3 km	1.9 km	6.2 km	10 km	19 km
15 megatonnes	Castle Bravo	4.2 km	5.1 km	16 km	32 km	49 km
50 megatonnes	Tsar Bomba	6.8 km	7.7 km	24 km	51 km	73 km

Swipe the table sideways to see every column.

Notice the pattern in the last two columns. For small weapons the blast reaches further than the heat; for large ones the heat overtakes it completely. A 50-megatonne weapon flattens houses to 24 km but burns people at 51.

What each ring on the map means

Fireball. The ball of gas hot enough to glow. Inside it, nothing survives in any recognisable form. If the weapon goes off high enough, the fireball never reaches the ground at all — which is exactly what happened over Hiroshima.

Overpressure rings. Overpressure is how much the air pressure jumps above normal when the shock front arrives, measured in pounds per square inch. At 20 psi almost every building fails. At 5 psi ordinary houses collapse — this is the contour that kills the most people, and it is the one weapons are fused to maximise. At 1 psi windows break, and flying glass injures people who never saw the flash.

Thermal rings. About a third of a nuclear weapon's energy leaves as light and infrared in the first few seconds. Third-degree burns mean burns through the full thickness of the skin. These rings are the ones that surprise people, because for large weapons they reach much further than the blast.

Prompt radiation. The neutron and gamma flash in the first minute. This is not fallout — it arrives at the speed of light, before the blast wave, and it stops as soon as the flash is over.

Air burst or ground burst: why it changes everything

This is the single most important setting in the simulator, and the one most people never touch.

When a weapon detonates in the air, the shock wave that travels down and bounces off the ground catches up with the shock wave travelling outward. The two merge into a single, stronger front called a Mach stem, which sweeps outward along the surface carrying roughly twice the pressure. Detonate at the right height and you place that merging exactly where you want the destruction. A 1-megatonne weapon burst at optimum height flattens houses out to 7.1 km; the same weapon detonated on the ground manages only about 5.7 km.

So an air burst destroys a substantially larger area — but it leaves no crater and produces very little fallout, because there is no soil sucked up into the fireball to be irradiated and rained back down. A ground burst does the opposite: less blast damage, a large crater, and heavy radioactive fallout downwind for days.

Both weapons used in 1945 were air bursts. Neither Hiroshima nor Nagasaki has a crater.

Does a nuclear bomb leave a crater?

Only if it goes off at or very near the ground. The Trinity test in 1945 — 21 kilotonnes on a tower — left a shallow bowl about 80 m across. Castle Bravo, a thousand times larger at 15 megatonnes, dug a crater 2 km wide and some 80 m deep in the reef at Bikini Atoll. Switch the simulator to a surface burst and it will show you the hole; leave it on air burst and there isn't one.

How far does the radiation reach — and when does it stop mattering?

Here is the least intuitive fact about nuclear weapons. For small weapons, the prompt radiation flash reaches further than the severe blast damage, so radiation is a leading cause of death. For a 15-kilotonne weapon the lethal radiation contour sits at about 1 km while the near-total destruction contour is at 0.5 km.

But radiation is absorbed by air, so its reach grows very slowly with yield, while blast and heat grow with the cube root. Somewhere around 100 kilotonnes the curves cross. Above that, everyone inside the lethal radiation radius has already been killed by the blast. For a megatonne-class weapon, prompt radiation adds essentially nothing to the death toll. The simulator tells you which regime you are in.

None of that applies to fallout, which is a separate and much longer-lasting problem, and which this tool deliberately does not model — see below.

What this simulator does not model

Being clear about the limits is part of being accurate.

Fallout. Where fallout goes depends entirely on the wind at several altitudes on the day. Drawing a plausible-looking plume without real weather data would be inventing a number, so we don't.

Shelter. Every figure assumes people are standing in the open. Being indoors, or below ground, changes survival dramatically — that is the entire basis of civil defence.

Time of day. The population data says where people live. A weapon used at three in the morning and one used at midday on a working weekday would kill very different people in very different places.

Fire. In some conditions the separate fires started by the flash merge into a firestorm that kills more people than the blast did. Whether that happens depends on how the city is built, and it cannot be predicted from yield alone.

A worked example of those limits. Put 15 kilotonnes over Hiroshima in the simulator and it estimates roughly sixteen thousand deaths. The real figure was about seventy thousand on the day. The model is not broken — it is answering a different question. It assumes the modern city, which is far less densely built than the 1945 one; it assumes reinforced concrete and modern glazing rather than timber and paper; and it does not model the firestorm that swept the city afterwards and killed more people than the blast wave did. Every simulator of this kind shares that gap. Treat the casualty figures as an order of magnitude, and the radii — which are physics — as the reliable part.

Where the numbers come from

The blast and thermal models are fitted to the standard tables in Glasstone & Dolan, The Effects of Nuclear Weapons (3rd edition, 1977), the US government's own unclassified reference, which has been public for almost fifty years. The blast curve reproduces the published 1-megatonne figures to within about ten per cent from 1 psi to 20 psi.

The best check on the model is one it was not fitted to. Nothing about burst height was tuned — yet if you ask the blast curve which height does the most damage with a 15-kilotonne weapon, it answers 577 metres. The weapon used over Hiroshima was fused for 580.

Prompt radiation is calibrated against the DS02 dose reconstruction for Hiroshima and Nagasaki. Cratering is fitted to the surveyed Trinity and Castle Bravo craters. Population comes from the GeoNames gazetteer and UN World Population Prospects, the same data behind our asteroid impact simulator.

This is a model of effects. It contains nothing whatsoever about how a weapon is designed or built; it starts from an energy release and works outward.

Common questions

How far away from a nuclear bomb is safe?

There is no single number, because it depends on the yield, the burst height, whether you are indoors and whether you can see the flash. For a 300-kilotonne air burst, someone outdoors 7 km away would probably survive the blast but could still receive serious burns. Beyond the 1 psi ring — about 13 km for that weapon — the main hazard is flying glass. Being inside, and especially below ground, changes the answer enormously.

Could a single bomb destroy an entire city?

A modern warhead flattens ordinary houses across a radius of four to six kilometres. That covers the core of most cities but not the whole built-up area. It is exactly why nuclear arsenals hold thousands of moderate warheads rather than a few enormous ones: because radius scales with the cube root of yield, many small weapons destroy far more total area than one huge one.

What is the difference between an air burst and a ground burst?

An air burst lets the reflected shock merge with the direct shock into a Mach stem, which roughly doubles the pressure sweeping outward — so it destroys a much larger area. It leaves no crater and very little fallout. A ground burst does about 20% less blast damage but excavates a crater and throws irradiated soil into the atmosphere, producing heavy fallout downwind. Both weapons used in 1945 were air bursts.

Does a nuclear bomb leave a crater?

Only if it detonates at or very near the ground. Trinity, 21 kilotonnes on a tower in 1945, left a shallow bowl about 80 m across. Castle Bravo at 15 megatonnes dug a crater 2 km wide in the reef at Bikini Atoll. Neither Hiroshima nor Nagasaki has one, because both were air bursts.

How far does nuclear radiation reach?

The prompt flash — neutrons and gamma rays in the first minute — reaches about a kilometre for a Hiroshima-sized weapon. Because air absorbs radiation, that range grows very slowly with yield while blast and heat grow with the cube root. Above roughly 100 kilotonnes everyone inside the lethal radiation radius has already been killed by the blast. Fallout is a separate matter entirely, and depends on the wind.

How accurate is this simulator?

The radii are reliable: the blast model reproduces the published 1 megatonne table to within about 10%, and asked which burst height does most damage with a 15 kilotonne weapon it answers 577 m, against the 580 m actually used over Hiroshima — a figure it was never fitted to. The casualty estimates are much softer. They count where people live rather than where they are, assume modern construction, and do not model firestorms.