The official currency of the United States and several other nations is the US dollar. The Coinage Act of 1792 established the United States dollar on par with the Spanish silver dollar, divided it into 100 cents, and permitted the minting of coins with dollar and cent values. Federal Reserve Notes, which are commonly referred to as "greenbacks" due to their predominately green tint, are the type of U.S. banknotes that are issued. The Federal Reserve System, which serves as the country's central bank, manages the monetary policy of the United States. A bimetallic standard of 371.25 grains of fine silver or, starting in 1837, 23.22 grains of fine gold, or $20.67 per troy ounce, was used to define the U.S. dollar at its inception. The dollar was exclusively linked to gold by the Gold Standard Act of 1900. Its conversion to gold was changed in 1934 to $35 per troy ounce. All ties to gold have been severed since 1971. After the First World War, the U.S. dollar emerged as a significant global reserve currency. The Bretton Woods Agreement, signed at the close of the Second World War, saw the dollar replace the pound sterling as the world's main reserve currency. The most popular and freely floatable currency in international trade is the dollar. Federal Reserve Notes are utilized in circulation, and it serves as both the official currency and the de facto currency of a number of other nations. On February 10, 2021, there were 2.10 trillion US dollars in circulation, $2.05 trillion of which were Federal Reserve Notes.