Of the total, 1,550 are in active service. Experts say that is enough to cause more than one billion deaths in the event of a nuclear war, although models on the severity of such a disaster vary widely.
A series of nuclear arms reduction treaties were agreed on at the height of the Cold War between the US and Communist Russia.
In 1969, the Strategic Arms Limitation Talks (Salt) and subsequent accords focused on limiting the number of nuclear weapons and methods of deployment, such as nuclear submarines and bombers.
Subsequent agreements such as Start, the Strategic Arms Reduction Treaty, were contentious for both sides and, by 1986, the combined nuclear arsenals of Russia and the US surpassed 70,000 weapons, according to the Federation of American Scientists.
But the agreements became the framework for post Cold War treaties, which sharply reduced nuclear weapon stockpiles.
US President Joe Biden is reversing course on former president Donald Trump’s policy of keeping the information from public knowledge.
Mr Trump also refused to renew the New Start treaty, intended to limit and reduce nuclear weapons stockpiles in Russia and the US, and pulled out of a separate agreement, the Intermediate-Range Nuclear Forces (INF) treaty.
The new disclosure, based on stockpiles held on September 30, showed that the US had reduced its inventory by 72 nuclear warheads since September 2017.
According to a 2018 study on potential nuclear conflict, scientists at the Michigan Technological University calculated that 100 nuclear weapons could kill at least 30 million people in the “initial blasts”.
Millions more would succumb to blast injuries and the effects of radiation.
Biden and Putin's nuclear pact
In June, Mr Biden and Russian President Vladimir Putin held a summit to discuss “future arms control and risk reduction measures”, according to a statement released after the meeting.
Mr Biden pledged to “work on a mechanism that can lead to control of new and dangerous and sophisticated weapons that are coming on the scene now that reduce the times of response, that raise the prospects of accidental war”.
The recent disclosure of US nuclear arms comes at a time when Russia and the US are discussing extending the New Start weapons reduction treaty.
Mr Trump said that he would not extend the treaty, which is scheduled to expire in February.
In New Start, Russia and the US agreed to limit their nuclear arsenals to 1,550 active weapons, while both sides also dismantled non-active weapons in their stockpiles.
One of Mr Biden’s first acts in office was to propose an extension to New Start. Russia quickly agreed and earlier this month, talks began in Geneva to create a successor to the treaty, which may be expanded to include limits on non-nuclear weapons.
"Increasing the transparency of states' nuclear stockpiles is important to nonproliferation and disarmament efforts," the State Department said after Tuesday’s disclosure.
According to data released under the New Start treaty in 2018, Russia maintains 1,444 active strategic nuclear warheads. The Stockholm Institute for Peace, a non-government organisation that monitors global conflicts, believes Russia’s nuclear arsenal, including retired weapons, could total more than 6,000 warheads.
But even these numbers pale in comparison with Cold War-era stockpiles. In 1967, at the peak of tensions between the US and the Soviet Union, the US arsenal numbered 31,255 warheads.
The current reduction in nuclear arms, to their lowest level on record, is hardly reassuring however.
Modelling the effects of a global nuclear conflict, the Natural Resources Defence Council calculated that a US attack on China with 789 nuclear warheads would kill 320 million people in the initial blasts, or about one quarter of China’s population, in 368 population centres.
A similar attack on the US with 124 warheads would also kill about one quarter of America’s 330 million citizens.