Decimal currency

Decimalisation is the process of converting a currency from its previous non-decimal denominations to a decimal system (i.e., a system based on one basic unit of currency and one or more sub-units, such that the number of sub-units in one basic unit is a power of 10, most commonly 100).

The only current non-decimal currencies are the Malagasy ariary (equal to five iraimbilanja) and the Mauritanian ouguiya (equal to five khoums), though in practice both just have one currency unit and no sub-unit because khoums and iraimbilanja are no longer minted.

Decimal currencies have sub-units based on a factor of 10. There are most commonly 100 sub-units to the base currency unit, but currencies based on 1000 sub-units also exist, especially in Arab countries.

For example:

Historically, non-decimal currencies were much more common: such as the British pound sterling before decimalisation in 1971. Until 1971, the pound sterling had sub-units of account of shillings (20 to a pound) and pence (12 to a shilling). Like other currencies, it also had coins with other names (ha'pence, guineas, and crowns); and in addition, until 1960 the penny was divided into 4 farthings. There were nineteen different fractions of a pound of a whole number of pence. For example, a third, quarter, fifth and sixth of a pound were respectively 80, 60, 48, and 40 pence, normally written as shillings and pence: 6/8, 5/-, 4/-, and 3/4. There were eight additional fractions which were a whole number of farthings (for example, one sixty-fourth of a pound was three pence three farthings, written  3 ³⁄₄d).

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