<P> After the Second World War, a system similar to a gold standard and sometimes described as a "gold exchange standard" was established by the Bretton Woods Agreements . Under this system, many countries fixed their exchange rates relative to the U.S. dollar and central banks could exchange dollar holdings into gold at the official exchange rate of $35 per ounce; this option was not available to firms or individuals . All currencies pegged to the dollar thereby had a fixed value in terms of gold . </P> <P> Starting in the 1959--1969 administration of President Charles de Gaulle and continuing until 1970, France reduced its dollar reserves, exchanging them for gold at the official exchange rate, reducing US economic influence . This, along with the fiscal strain of federal expenditures for the Vietnam War and persistent balance of payments deficits, led U.S. President Richard Nixon to end international convertibility of the U.S. dollar to gold on August 15, 1971 (the "Nixon Shock"). </P> <P> This was meant to be a temporary measure, with the gold price of the dollar and the official rate of exchanges remaining constant . Revaluing currencies was the main purpose of this plan . No official revaluation or redemption occurred . The dollar subsequently floated . In December 1971, the "Smithsonian Agreement" was reached . In this agreement, the dollar was devalued from $35 per troy ounce of gold to $38 . Other countries' currencies appreciated . However, gold convertibility did not resume . In October 1973, the price was raised to $42.22 . Once again, the devaluation was insufficient . Within two weeks of the second devaluation the dollar was left to float . The $42.22 par value was made official in September 1973, long after it had been abandoned in practice . In October 1976, the government officially changed the definition of the dollar; references to gold were removed from statutes . From this point, the international monetary system was made of pure fiat money . </P> <P> An estimated total of 174,100 tonnes of gold have been mined in human history, according to GFMS as of 2012 . This is roughly equivalent to 5.6 billion troy ounces or, in terms of volume, about 9,261 cubic metres (327,000 cu ft), or a cube 21 metres (69 ft) on a side . There are varying estimates of the total volume of gold mined . One reason for the variance is that gold has been mined for thousands of years . Another reason is that some nations are not particularly open about how much gold is being mined . In addition, it is difficult to account for the gold output in illegal mining activities . </P>

When did us stop being backed by gold