In the early days of the United States, the term "Dollar" was commonly known as a coin minted by Spain called the Spanish Milled Dollar.

In the early days of the United States, the term "Dollar" was commonly known as a coin minted by Spain called the Spanish Milled Dollar. These coins were the standard money then in use in the country. On April 2, 1792, Alexander Hamilton, then the Secretary of the Treasury, made a report to Congress having scientifically determined the amount of silver in the Spanish Milled Dollar coins that were then in current use by the people. As a result of this report, the Dollar was defined as a unit of measure of 371 4/16th grains of pure silver or 416 grains of standard silver (standard silver being defined as 1,485 parts fine silver to 179 parts alloy). Therefore paper is not the dollar, instead, it is 'worth', not 'is', 1 dollar (US Silver certificate.) In section 20 of the Act, it is specified that the "money of account" of the United States shall be expressed in those same "dollars" or parts thereof. All of the minor coins were also defined in terms of percentages of the primary coin — the dollar — such that a half dollar contained 1/2 as much silver as a dollar, quarter dollars contained 1/4 as much, and so on.

In an act passed on January 18, 1837, the alloy was changed to 10%, having the effect of containing the same amount of silver but being reduced in weight to 412 1/4 grains of standard silver which was changed to 90% pure and 10% alloy. On February 21, 1853 the amount of silver in the fractional coins was reduced so that it was no longer possible to combine the fractional coins to come up with the same amount of silver that was in the dollar.

Various acts have been passed over the years that affected the amount and type of metal in the coins minted by the United States such that today, there is no legal definition of the term "Dollar" to be found in any Statute of the United States.

Today, the closest definition to a dollar comes from the United States code Title 31, Section 5116, paragraph b, subsection 2, "The Secretary [of the Treasury] shall sell silver under conditions the Secretary considers appropriate for at least $1.292929292 a fine troy ounce." However Federal Reserve banks are only prejudiced to deliver tax credits instead of money. The silver content of US coinage was mostly removed in 1965 and the dollar essentially became a baseless free-floating fiat currency, though the US Mint continues to make silver $1 bullion coins at this weight.

Continued Chinese demand for silver led several countries, notably the United Kingdom, United States, and Japan, to mint trade dollars in the 19th and early 20th centuries, often of slightly different weights to their domestic coinage. Silver dollars reaching China (whether Spanish, Trade, or other) were often stamped with Chinese characters known as "chop marks", which indicated that that particular coin had been assayed by a well-known merchant and determined genuine.