There are seven denominations of Canadian coinage circulating: 1¢, 5¢, 10¢, 25¢, 50¢, $1, and $2. Though officially titled the One Cent Piece, Five Cent Piece, Ten Cent Piece, Twenty-Five Cent Piece, Fifty Cent Piece, One Dollar Coin and Two Dollar Coin; they are colloquially referred to as the penny, nickel, dime, quarter, half-dollar, loonie, and toonie respectively. The Fifty Cent Piece, though in circulation, is far less circulated than the other coins. Between the years 2000 and 2007 the Royal Canadian Mint struck 15,950,000 Fifty Cent Pieces; in comparison, during the same period 2,262,165,000 Twenty-Five Cent Pieces were released (approximately 142 times as many).
Other than the Two Dollar Coin, the denominations of Canadian coinage correspond to those of United States coinage. The sizes of the coins less than 50¢ are similar to those of U.S. coins, though this was not always the case. While the coins tend to have diameters almost equal to the equivalent U.S. coinage, most of the coins are thinner and weigh less than the equivalent U.S. coinage. The US penny settled on its current size in 1857, whereas the Canadian penny was much larger (25.4 mm) until 1920. There was some correspondence between the size of Canadian coins and British coins of similar value. For example, the large Canadian penny was identical in size and value to the contemporary British half-penny, which were 25.4 millimetres in the Edward VII version, and slightly larger during Victoria's reign. Likewise, the Canadian quarter (23.81 mm diameter) was virtually identical in size and value to theBritish shilling (worth ~24 Canadian cents, or 12 British pennies, with a 24 mm diameter). The Canadian 5 cent coin, until the larger nickel coins of 1922, were 15 mm silver coins quite different from the US Liberty Head Nickels of 1883-1913, which were 21.2 mm and copper/nickel alloy.
Modest quantities of U.S. coinage circulate in Canada at par, and some Canadian coins (generally those with value less than fifty cent) circulate in the United States as well, though recent changes to the appearance and composition of Canadian coinage have made acceptance of these coins by merchants in the United States less certain. This partial interchangeability led to some concern when the United States Mint decided that the new Sacagawea Dollar coin would have the same diameter and colouring as the Canadian $1 coin, the "loonie", although this proved to be a non-issue.