The Largest Nuclear Bombs Ever Tested: Top 10 Explosions by Yield

The largest nuclear bomb ever detonated was the Soviet Union’s Tsar Bomba, set off over the Arctic island of Novaya Zemlya on October 30, 1961, with a yield of about 50 megatons, roughly 3,300 times the bomb dropped on Hiroshima. Nothing before or since has come close. But the Tsar Bomba was the peak of a short, frantic period in which the United States and the Soviet Union tested dozens of multi-megaton weapons, and the full list says more about the Cold War than any single blast. According to the Arms Control Association, the world has conducted more than 2,000 nuclear tests since 1945.

The 10 largest nuclear explosions ever tested

Yields are given in megatons of TNT equivalent (1 megaton equals 1,000 kilotons). Some Soviet figures come from declassified Russian records and carry a margin of error. For scale, the Hiroshima bomb released about 15 kilotons.

Two things stand out. First, every one of the ten largest tests was carried out by one of two countries, in a window of barely a decade. Second, most of them happened in 1961 and 1962, the months around the Berlin crisis and the Cuban Missile Crisis, when both governments treated test yields as a form of public messaging.

Tsar Bomba: why the biggest bomb was deliberately cut in half

The Tsar Bomba was designed for about 100 megatons. Soviet physicists, including Andrei Sakharov, reduced it to roughly half by replacing part of the fusion fuel’s uranium tamper with lead. The reasons were practical: a full-yield test would have spread enormous amounts of fallout over Soviet territory, and the modified Tu-95 bomber that dropped it would likely not have escaped the blast.

Even at half power, the fireball was visible from about 1,000 kilometres away, windows broke hundreds of kilometres from ground zero, and the mushroom cloud rose to roughly 60 kilometres. We cover the physical effects in detail, including the seismic signal and how far the shockwave travelled, in our separate article on the Tsar Bomba’s shockwave, earthquake magnitude and aftermath.

Castle Bravo: the biggest American test was an accident

The largest nuclear bomb the United States ever detonated was never meant to be that large. Castle Bravo was expected to yield about 6 megatons. It produced 15, because designers had underestimated how much the lithium-7 in the fuel would contribute to the reaction.

The miscalculation had real victims. Fallout drifted over inhabited atolls in the Marshall Islands and onto the crew of a Japanese fishing boat, the Daigo Fukuryu Maru, about 130 kilometres away. One crew member later died. The episode fed the international campaign that eventually produced the 1963 Partial Test Ban Treaty, which moved testing underground.

The largest nuclear bomb tested by each country

Only the two superpowers ever went above 10 megatons. The other nuclear powers built much smaller arsenals and stopped at a few megatons, or never built thermonuclear weapons at all.

North Korea’s largest test, in September 2017, is usually estimated at roughly 100 to 250 kilotons. That is large by modern standards, but still a fraction of one megaton.

Why nobody builds bombs that big anymore

The race to ever-bigger yields ended quickly, and not mainly for moral reasons. Blast damage does not scale in a straight line with yield: the radius of destruction grows roughly with the cube root of the energy released. A bomb eight times more powerful only destroys an area about four times larger. Much of the extra energy of a giant weapon goes straight up into the atmosphere.

At the same time, missiles became far more accurate. Several smaller warheads on a single missile could cover more ground, and hit specific targets, better than one enormous bomb. Most warheads in today’s arsenals have yields from tens of kilotons to a few hundred kilotons. The Tsar Bomba itself was too heavy to be a practical weapon; it was a demonstration.

Treaties did the rest. The 1963 Partial Test Ban Treaty banned tests in the atmosphere, underwater and in space. The 1974 Threshold Test Ban Treaty between Washington and Moscow capped underground tests at 150 kilotons. The Comprehensive Nuclear-Test-Ban Treaty was opened for signature in 1996 and, although it has not formally entered into force, it has held the major powers to a testing moratorium for three decades.

Canada’s place in the nuclear story

Canada never tested a nuclear weapon, but it was closer to the bomb than many Canadians realise. Uranium from the Eldorado mine at Port Radium, on Great Bear Lake in the Northwest Territories, went into the Manhattan Project during the Second World War.

During the Cold War, American nuclear warheads were stationed on Canadian soil. The issue split the country in the 1963 federal election: John Diefenbaker’s government had accepted Bomarc anti-aircraft missiles but hesitated to arm them, while Lester Pearson’s Liberals promised to accept the warheads and won. The first warheads arrived at RCAF Station North Bay on New Year’s Eve 1963. Pierre Trudeau’s government later phased the weapons out; the Bomarcs were retired in the early 1970s, and the last nuclear weapons, Genie air-to-air rockets carried by CF-101 Voodoo fighters, went back to the United States in 1984. Canadian scientists also operate part of the global network of seismic and radionuclide stations that monitors compliance with the test ban today.

Frequently asked questions

What is the largest nuclear bomb in the world?

The largest nuclear bomb ever detonated is the Soviet Tsar Bomba, tested on October 30, 1961, at about 50 megatons. It was designed for 100 megatons but deliberately scaled down. No larger weapon has ever been tested.

What is the biggest nuclear bomb the United States ever tested?

Castle Bravo, detonated at Bikini Atoll on March 1, 1954, with a yield of 15 megatons. It was expected to yield about 6 megatons, and its unexpected power caused serious fallout on nearby islands.

How much stronger was the Tsar Bomba than Hiroshima?

Roughly 3,300 times. The Hiroshima bomb released about 15 kilotons of energy, while the Tsar Bomba released about 50,000 kilotons.

Are today’s nuclear bombs bigger than the Tsar Bomba?

No. Modern warheads are far smaller, usually tens to hundreds of kilotons. Military planners favour accuracy and multiple warheads over sheer size, because blast damage grows much more slowly than yield.

Did Canada ever have nuclear weapons?

Canada never built its own, but American nuclear warheads were deployed with Canadian forces from the end of 1963 until 1984, on Bomarc missiles and later on Genie rockets carried by CF-101 Voodoo fighters.