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Historically, non-decimal monetary systems were common. E.g. pound / shilling.

Every currency I can think of or have ever used is 'decimal' (where a higher/lower unit of currency is either a multiple or factor of 10).

Are all currencies used by countries nowadays 'decimal'?

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stevec
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    By the definition you provided (all of the currency is either a multiple or factor of 10), is the US dollar even a decimal currency? We have quarters, which are neither a multiple or factor of 10. Or am I missing something? – bvoyelr Jan 07 '20 at 13:55
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    @bvoyler. Yes, you are missing that a quarter is 25 cents. The cent is a unit of currency, a quarter is just a denomination of coins. I.e the price of something wouldn’t be described as “2 quarters” but as “50 cents”. – Darren Jan 07 '20 at 14:54
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    @Darren AHHH! Now it's coming together. I shouldn't think this much so soon after Christmas vacation. – bvoyelr Jan 07 '20 at 18:21
  • Is a cent a unit of currency, or is it one per cent of a unit of currency? I'm skeptical that 25 fits into a 'decimal' based system in either case. – Mooing Duck Jan 07 '20 at 21:39
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    @MooingDuck If a currency had 100 cents to the dollar and a 3 cent coin, it would still be decimal because the two units (cents and dollars) have a ratio that is a power of 10. – CJ Dennis Jan 07 '20 at 23:19
  • @CJDennis: The USD Unit is a dollar, not a cents. However: Nobody sells things in counts of quarters either, invalidating my point, I think. People use dollars and/or cents to discuss prices, not nickels, dimes, or quarters. So I stand corrected, and agree that USD is a decimal system. – Mooing Duck Jan 07 '20 at 23:31
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    @MooingDuck If you like, the cent is a sub-unit of the dollar. A quarter is then a multiple of a cent, not a sub-unit of the dollar. :-) – CJ Dennis Jan 07 '20 at 23:35
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    The better counter argument is a price can be "50 cents" but a price is never* "2 quarters". *except in arcades, where physical quarters become a separate currency than monetary value. – Mooing Duck Jan 07 '20 at 23:52
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    What about 17 Sickles to a Galleon and 29 Knuts to a Sickle? Does that count? – Kevin Jan 08 '20 at 00:08
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    Prices are not indicated in dollars, quarters and cents (say, $1, 2q, 4¢, read out as "one dollar, two quarters, 4 cents", similar to the British pre-decimal system), but in dollars ($1.54) or in dollars and cents ("one dollar and 54 cents"). – dgstranz Jan 08 '20 at 09:00
  • We are all on the same page. But I've now figured out how to articulate my initial confusion: Darren was working with the concept that a cent is a unit of currency and a quarter is not, and I didn't immediately see why that was a valid assumption. I worked it out eventually. – Mooing Duck Jan 09 '20 at 07:04
  • IIUC Yen have subdivisions of 1/100 and 1/1000, but practically the yen is the lowest denomination you could see on the street. You don't get change in sen and rin. Why doesn't yen count? – kojiro Jan 09 '20 at 11:43
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    @CJDennis True but origin of the quarter is based on dividing a coin into eighths: "shave and a haircut, two bits" Quarters are a somewhat weird denomination. We don't have 25 dollar bills. – JimmyJames Jan 09 '20 at 21:07

3 Answers3

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The word you're looking for is not "metric" but "decimal".

Pretty much all currencies are decimal these days except for currencies that have divisions where the sub-unit is no longer used as it's worth so little.

The only countries left with non-decimal currencies are Mauritania and Madagascar according to wikipedia

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    With OP's definition, Mauritania and Madagascar are metric/decimal, too, since 5 is a factor of 10. – Federico Poloni Jan 07 '20 at 17:49
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    @FedericoPoloni That does not make them decimal. Two hundred and twenty in a decimal system would be written 2 dollars 20 cents (which looks like 220) but in the Mauritanian system would be 44 dollars (which looks nothing like 220) – slebetman Jan 09 '20 at 02:04
  • @slebetman "Looks like 220" this is not how OP defined "decimal". It is a higher/lower unit of currency is either a multiple or factor of 10. – Federico Poloni Jan 09 '20 at 07:30
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    @FedericoPoloni It is how the OP defined decimal. You seem to understand it is the multipe is a factor of 10 but he said the multiple or factor is 10 – slebetman Jan 09 '20 at 07:40
  • @slebetman I am interpreting what OP wrote as "a monetary system is decimal if, given two successive currency units (for instance dollars and cents), one is N times the other, where N is either a multiple or an integer divisor of 10". What is your proposed interpretation exactly? Sorry but neither of those two expressions you wrote is clear to me. – Federico Poloni Jan 09 '20 at 07:55
  • If I understand correctly, your interpretation is "a monetary system is decimal if, given two successive currency units (for instance dollars and cents), one is N times the other, where N is 10", because "multiple or factor" in your interpretation refers to the fact that the two units may be one a multiple or a factor of the other, depending on the order in which they are considered. But with this definition, the US system is not decimal, because the only two currency units are dollars and cents, which have a ratio of 100, not 10. "Dec", or 1/10 of a dollar, is not a currency unit in use. – Federico Poloni Jan 09 '20 at 08:00
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    OP's definition of "decimal" is unclear, doesn't seem to be consistent with what is normally called "decimal" (e.g. by @FedericoPoloni's interpretation (which I think is a reasonable literal interpretation), hours (or degrees), minutes and seconds would be decimal, but these wouldn't usually be called a decimal system), and probably is not what they actually meant. I think what most people would understand by a decimal system would be: "a monetary system is decimal if it has two or more units, where the value each unit is an integer power of 10 times the value of each other unit." – John B. Lambe Jan 09 '20 at 12:59
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    @JohnB.Lambe because the question originally used the word "metric" as the OP's understanding of terminology was unclear. Someone changed metric to decimal throughout the question but the definition was still the OPs original definition of "metric" – Robert Longson Jan 09 '20 at 13:03
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The Wikipedia article Non-decimal currency explains the situation in full:

Today, only two countries have non-decimal currencies: Mauritania, where 1 ouguiya = 5 khoums, and Madagascar, where 1 ariary = 5 iraimbilanja. However, these are only theoretically non-decimal, as in both cases the value of the main unit is so low that the sub-units are too small to be of any practical use and coins of the sub-units are no longer used.

The official currency of the Sovereign Military Order of Malta, which retains its claims of sovereignty under international law and has been granted permanent observer status at the United Nations, is the Maltese scudo, which is subdivided into 12 tarì, each of 20 grani with 6 piccioli to the grano.

All other contemporary currencies are either decimal or have no sub-units at all, either because they had been abolished or because they have lost all practical value and not used.

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    That Maltese one is weird... It's like an alternative version of the old British system of the Pound, which was subdivided into 20 shillings, each of 12 pennies, with 4 farthings to the penny. – Oscar Bravo Jan 08 '20 at 11:19
  • @Oscar It has nothing to do with older British currency, except for being non-decimal... – Lightness Races in Orbit Jan 08 '20 at 18:25
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    Note that base 12 divides very well by 1/2/3/4/6/12 and that makes 'scudo' easy to divide by that numbers (i.e. split 1 scudo over 6 people evenly). At 'grani' level it makes it easy to divide by 5 (20=522). I have no idea why 3rd level (piccoli) was added, maybe grani was too big at some time in history, but it's base 6, so makes 'grani' divisible by 1/2/3. btw:Note how hours/minutes/seconds system is itself base-60 (512 - see 12?),and days/hours is base-24 (212 - see 12?) - again because it makes it easy to divide. Base-10 systems make it pretty hard to divide 100$ over 3 people evenly.. – quetzalcoatl Jan 08 '20 at 18:39
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    Which explains why there are 36 numbers on a roulette wheel ;-) Now, if only I could find a casino which will accept my scudi ... – Mawg says reinstate Monica Jan 09 '20 at 06:56
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    Interesting that only 60 years ago, the GBP was divisible into 960 parts, and only 50 years ago was still divisible into 480 (halfpennies). How soon before even 100 divisions is deemed too many..? – Tim Jan 09 '20 at 10:04
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    @Tim there was some discussion on this in the UK not too long ago, in case you're interested https://www.bbc.co.uk/news/business-48133093 – Max Jan 09 '20 at 13:32
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What about Japan? AFAIK the yen is not subdivided into lesser units, nor is it a subdivision of a larger unit. Even if denominations are issued in multiples of 10**n yen, that is arbitrary and doesn't fundamentally make the yen a decimal currency.

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