A Conundrum If Ever There Was One

Last I checked.

Most if not all of the world coinages were originally NON-decimal, and they started changing over in the late 1700s. The UK and a few other places were the last holdouts when they switched in the 1960s.

China was decimal for well over a millenium AFAIK, though they cheated a bit because for most of that time their main unit was so low they never had to deal with fractions. Russia went decimal in the 1535 reform (though the larger denomination was a unit of account and not yet minted at the time) and then got that confirmed in the 1700 reform. IIRC there are one or two other sporadic cases of early decimalization.

Other than that, though, yeah, pretty much. AFAIK the USA, in 1792 (or so), was actually the first of the main wave of decimalization.
(IIRC US coinage used to be literally decimal, with factors of 10 everywhere: 10 mills = 1 cent, 10 cents = 1 dime, 10 dimes = 1 dollar, 10 dollars = 1 eagle. The next unit up is called a "union" but was only minted in very rare patterns. AFAIK there is no conventional name for the next unit down, but I like Mark Twain's suggestion of "milray".)

The ancient Romans were the first to use something resembling a decimal system, though it was largely by accident rather than an intent to "go decimal".

The basic Roman monetary unit was the copper "as". In the Early Imperial period, there were four asses to the sestertius (which was the money of account), four sestertii to the denarius, and 25 denarii to the gold aureus. Thus, an aureus was worth 100 sestertii. This ratio remained in place until the value of the denarius collapsed in the mid-200s AD.

In the earlier Republic period, the denarius was originally worth 10 asses - its name literally means "worth 10 asses", and early denarii bore the denomination-mark "X" for 10. In 141 BC, the face value was increased to 16 asses, though the name remained the same.

Don't forget, people back then didn't have a base-10 numeral system (1, 2, 3, etc). Mathematics had to be done using Roman numerals, which was cumbersome - so it didn't really matter whether the currency was in base 10 or not, the maths would be just as hard.


The Americans may have been the first (apart from the Russians), but it was the French coming second, in 1795, that decimalized the world.

Revolutionary France decimalized everything - all units of distance, weight and even time (though the decimal clock and decimal calendar never really took off). It was all part of the revolutionary doctrine, of throwing out the old and replacing it with the new. Money was just one small part of the decimalization craze.

And it is the French you can thank for forcing the rest of Europe to go decimal; when France conquered most of Europe, they enforced the French standards of weights, including money. Most of the places France conquered never bothered re-instating their old currencies and units of measure after they regained independence. And guess which piece of Europe was never conquered by revolutionary France? That's right, Britain - the only non-Metric, non-Decimal holdout.

As for why America adopted decimal currency, it was partly for alignment with Revolutionary France, and partly for the same reason the French found: throwing out the old symbols of the old regime. Unlike weights and distance, the revolutionary Americans had to get rid of the old British currency, because it was covered in Royalist symbolism. And if you're going to go to all the trouble of replacing all the coins, you might as well reform the currency to something more logical while you're at it.

That it wasn't really a matter of mathematical convenience or necessity that drove the decision, can be seen in the continuation of the non-metric fraction of the quarter-dollar. Quarter-dollars were already in circulation, thanks to the prevalence of Spanish colonial coins in trade. The belated attempt to replace the quarter with a 20 cent piece in the 1870s was too little, too late. The American currency system remains on a quasi-decimal basis as a result.

Papal States has both the U.S. and France beat by more than 50 years.

100 baiocchi = 1 scudo, at least by 1721 in some places under Vatican rule, and everywhere by the 1740s.
https://en.numista.com/catalogue/pieces239260.html

A very interesting topic.


For a few years in grade school we were all about the metric system and how it would be what we would use in our adult lives. Then they totally changed course and pretended the previous years' lessons had never happened.

The US counting system is decimal, but the underlying metals content is not. IMO for silver it's based on the Spanish base 8 system which was used heavily in the US until the 1850's. The quarter is popular as the equivalent weight of dos reales, hence "two bits". The French in contrast decimalized their weights and counting, with the silver franc weighing 5 grams.

Gold counting is decimalized too, but the weight basis is more complicated. The English system was a royal mess for centuries, but it standardized on the guinea in the mid 1600's. A guinea is very close in weight to the US half eagle (and later the UK sovereign). The Spanish base 8 system gold counting system doesn't really enter in (except for the Brasher doubloon). The Spanish half escudo is very close to the weight of a US gold dollar, so might be considered a starting point for US counting decimalization.