Nuclear weapons are straight-up terrifying and one of those brutal facts of life most of us try to forget for our own sanity. The bomb that fell on Hiroshima, ironically called Little Boy, produced an explosion of 15 kilotons (or the equivalent of 13,600 tonnes (15,000 US tons) worth of TNT). The one on Nagasaki was 21 kilotons.
That was over 60 years ago and nukes have only become more and more powerful in the intervening years. Today, the most powerful bomb ever detonated was called the Tsar Bomba. The USSR tested out this monstrosity in 1961. It has a force of 50 megatons, which is equivalent to 3,333 Little Boys or 45 million tonnes (50 million US tons) of TNT.
If one of these Tsar Bombas were to be detonated on Washington DC, the blast would extend all the way to Baltimore. Perhaps then, we should be grateful that Russians nixed plans for an even larger bomb, which would have had twice the power of the Tsar Bomba.
The largest nuclear weapon to be tested in the US is the 15 megaton Castle Bravo, detonated in 1954. The bomb was released above Bikini Atoll in the Marshall Islands, right in the middle of the Pacific Ocean, but the nuclear fallout from the blast was detected across the globe, from Japan to Europe.
Mercifully, the Castle Bravo is no longer in the US arsenal. The most powerful nuke the US is currently in possession of is the B38, which is 1.2 megatons. While this makes it quite a bit smaller than the Tsar Bomba and the Castle Bravo, it still has the explosive power of 1 million tonnes (1.2 million US tons) of TNT (or 80 Little Boys).
All in all, there are roughly 15,000 nuclear weapons in existence today, controlled by nine countries. These nine countries are the US, Russia, the UK, France, China, India, Pakistan, Israel, and North Korea. South Africa is the only country (so far) to have built and then voluntarily dismantled a nuclear weapon programme.
The number of weapons in existence today are enough to destroy the planet dozens of times over though experts say that if just five nuclear weapons were detonated, the world could be plunged into a nuclear autumn. This is a period of significant cooling that would result in a huge amount of destruction to both land and sea environments. It is not quite as severe as a nuclear winter.
Watch this video by RealLifeLore for more information on the true scale of nuclear weapons.