The nuclear-weapon states are the five states—China, France, Russia, United Kingdom, and the United States—officially recognized as possessing nuclear weapons by the NPT. […] Most of the figures below are best estimates of each nuclear-weapon state’s nuclear holdings, including both strategic warheads and lower-yield devices referred to as tactical weapons. Russia and the United States also retain thousands of retired warheads planned for dismantlement, not included here.
China: About 240 total warheads.
France: Fewer than 300 operational warheads.
Russia: Approximately 5,500 total warheads: 1,492 operational strategic warheads, approximately 2,000 operational tactical warheads (not deployed), and approximately 2,000 reserve warheads in storage.
United Kingdom: Fewer than 160 deployed strategic warheads, total stockpile of up to 225.
United States: Approximately 5,000 total warheads: 1,737 deployed strategic warheads, approximately 500 operational tactical weapons (some 200 deployed in Europe), and approximately 2,700 reserve warheads (active and inactive) in storage.
Three states—India, Israel, and Pakistan—never joined the NPT and are known to possess nuclear weapons. […]
India: Up to 100 nuclear warheads.
Israel: Between 75 to 200 nuclear warheads.
Pakistan: Between 90 to 110 nuclear warheads.
North Korea: Has separated enough plutonium for roughly 10 nuclear warheads.
How many times over could the world’s current supply of nuclear weapons destroy the world?
None. Zero. As in: We don’t have enough nukes.
Today the notion of all-out nuclear war is rarely discussed. There are concerns about Iran and North Korea’s nuclear programmes and fears that terrorists might get hold of a nuclear bomb. But the fear of a war in which the aim is to wipe out the entire population of an enemy has startlingly diminished.
In 1962, the concept of mutually assured destruction started to play a major part in the defence policy of the US. President Kennedy’s Secretary of Defense, Robert McNamara, set out in a speech to the American Bar Foundation a theory of flexible nuclear response.
In essence it meant stockpiling a huge nuclear arsenal. In the event of a Soviet attack the US would have enough nuclear firepower to survive a first wave of nuclear strikes and strike back. The response would be so massive that the enemy would suffer “assured destruction”.
Thus the true philosophy of nuclear deterrence was established. If the other side knew that initiating a nuclear strike would also inevitably lead to their own destruction, they would be irrational to press the button.