Decimal currency is the term used to describe any currency for which the ratio between the basic unit of currency and its sub-unit is a power of 10.

In practice this usually means that 100 sub-units make up 1 of the basic units, but currencies divided into 1000 sub-units also exist, especially in Arab countries.

For example:

• 100 United States cents make one dollar
• 100 British pence make one pound
• 100 "euro cent" make one euro
• 1000 Tunisian millimes make one dinar
• 100 Paise make one Rupee

Today, the only currencies which are not decimal are those that have no sub-units at all, plus;

• the Mauritanian ouguiya, 1 ouguiya = 5 khoum, and
• the Malagasy franc of Madagascar: 1 ariary = 5 Malagasy francs. The latter currency is doubly unusual: note that the "default" unit is actually the smaller unit.

Historically, non-decimal currencies were much more common, such as the British pound sterling before decimalisation in 1971. Once the world's leading currency, the pound sterling worked on a system of pence (12 to a shilling) and shillings (twenty to a pound), plus other combinations (ha'pence, tuppence, guinea, and crown).

However, the rise of the dollar as the most common world currency in the second half of the twentieth century, and the convenience of decimalized currency for electronic transactions, has led to the domination of the decimalized currency.