Although the vast majority of coins are round, coins are made in a variety of other shapes, including squares, diamonds, hexagons, heptagons, octagons, decagons, and dodecagons. They have also been struck with scalloped (wavy) edges, and with holes in the middle. Coins in the shape of polygons often have rounded edges or are Reuleaux polygons.
This article focuses mainly on circulating coins; a number of non-circulating commemorative coins have been made in special shapes, including guitars, pyramids, and maps. There is a list with more unusual shapes of non-circulating commemorative coins at the end of this page, that all have been issued officially by various countries.
Many countries have struck square coins with rounded corners. Some of these, such as the Netherlands zinc 5 cent coin of World War II (1941-1943) and the Bangladesh 5 poisha coin (1977-1994) are oriented as a square, while others, such as the Netherlands 5 cents (1913-1940), the Netherlands Antilles 50 cent, the Bangladesh 5 poisha (1973-1974) and the 1981 Jersey 1 pound coin, are oriented as a diamond. Ceylon (the current Sri Lanka) issued its first square coin in 1909, followed by several others. India has had various circulating square coins as well, like denominated 1/2 and 2 anna coins, as well as 1 and 5 paisa coins.
The Mutawakkilite Kingdom of Yemen introduced pentagonal 1⁄16 and 1⁄8 rial coins in 1948. In 2014 Transnistria was the next country to issue a circulating pentagonal 5 rubles hard plastic coin.
The Belgian Congo had a hexagonal 2 franc coin, as did the Kingdom of Egypt (2 piastres, also known as 2 qirsh). India used to have 3 paise and 20 paise coins that were hexagonal with rounded corners. The Burma (25 pyas) is scalloped hexagonal.
The Madagascar 10 ariary coin is seven-sided. The British twenty pence and fifty pence coins are heptagonal Reuleaux polygons, as is the United Arab Emirates 50 fils coin, the Barbados one dollar coin, and several coins from Botswana. Many countries in the Commonwealth of Nations have issued heptagonal coins. Reuleaux polygons have constant width, which means the currency detectors in coin-operated machines do not need an extra mechanism to detect shape.
The Chile 1 peso and 5 pesos coins issued from 1992 to 2015 are eight-sided. So was the old circulating Malta 25 cent coin commemorating Malta's first anniversary of the republic and some California gold coins. Some other countries that have issued circulating octagonal coins are the Lebanon and Sierra Leone.
In 1972 the first country to issue a circulating nine-sided coin was Thailand with a 1972 regular 5 baht coin, followed by Kenya in 1973 with a special issue 5 shillings coin. The third and final circulating nonagonal coin issued in the 20th century and is the regular 1976 50 cent coin from Tuvalu. Currently, the Philippines issues nonagonal 5-peso coins from 2019 as an enhanced design of the round version to make it distinct from the other denominations.
Hong Kong issued a ten-sided 5 dollar coin from 1976 to 1979, while the Philippines issued ten-sided two piso (peso) coins from 1983 to 1990. Some other countries that have issued ten-sided circulation coins are Chile, the Dominican Republic, Jamaica and Madagascar.
Many countries have struck twelve-sided coins, mostly countries belonging to the Commonwealth of Nations. Several of these are 3 pence (or quarter shilling) coins from the pre-decimal pound. Coins currently circulating include the British one pound coin, 50 cent coins from Australia, Fiji and the Solomon Islands, the Tongan 50 seniti coin and the circulating commemorative Croatian 25 kuna coins.
Many countries have coins with scalloped (wavy) edges. These usually have twelve bumps (e.g. the Vanuatu 100 vatu or the Hong Kong 20 cents), but can have other numbers such as eight (the eSwatini 10 cents or the Ang Bagong Lipunan Philippine five centavo coin) or sixteen (the Libya 50 dirhams).
Often a round coin will have a central hole. In some countries this was to allow them to be strung together, while other reasons include difficulty of counterfeiting and ability for visually impaired people to distinguish them from other coins.
Some coins give the impression that holes were used to save metal, though it may not be possible to prove with certainty that this was the reason for creating the holes. An example of such a coin with a fairly large hexagonal hole is a undated tin 1 cash coin, minded in the period 1550-1596, that circulated in the Banten Sultanate on Java and Sumatra (Indonesia). Also, several tin 1 pitis coins with exceptionally large round holes, of which some were made in octagonal coins, were used in Jambi Sultanate on Northern Sumatra (Indonesia). Due to the soft metal tin used to make these thin old coins, they can easily be bent. In the years 1943-1947 India produced 1 pice coins for circulation with very large holes, continued by Pakistan producing 1 pice coins of equal shape in the years 1948-1952.
Half circle: for Barbados Spanish coins were cut in half, it is hard to detect originals though, many forgeries exist.
Triangular: Bermuda has some special issue triangular coins from 1997 onward with curved edges. The Isle of Man has some triangular special issue coins where the triangle is not regular (the angles are not all 60 degrees).
Tetradecagonal: In 1976, Malaysia was the first country to issue 14-sided coins, the non-circulating 10 (silver) and 200 (gold) ringgit. Australia started to issue a series of non-circulating 14-sided 50 cents coins dedicated to the Chinese zodiac in 2012.
Quarter circle: Poland has issued a 10 z?otych coin in the shape of a quarter circle.
Spheres: Niue issued the first official (non-circulating) spherical coin with a face value of 7 New Zealand dollars. Several other countries followed soon with spherical coins, like Poland and Barbados. A 2008-2014 1 dollar sphere issue from Somalia is considered a fantasy coin, it was not officially issued by Somalia.
Yin Yang: Fiji has issued some Yin Yang shaped coins.
Arc (section of a circle with a hole): China started to issue a series of arc-shaped coins in the year 2000.
Heart: Several countries have issued non-circulating heart shaped coins, like China, Cook Islands and Poland.