Why Do the French Do Maths When Counting?

Why in France do we say une douzaine d'œufs, and not just ten, or quatre-vingt-dix for 90, and not just neuvante? If you've ever felt confused by French numbers, you're not alone. Let's dive into the surprising history behind these odd ways of counting.

A Dozen Oysters, Not Ten

Have you ever noticed that eggs and oysters are bought by the dozen? But why? Why not by ten or not by six? Always twelve! Well, be it in France or other part of the world, this is not just a food thing. It is math. Or more precisely, history.

The number 12 used to be a base for counting. It made sense: 12 is divisible by 2, 3, 4 and 6. Try this: take your thumb, use it to count the phalanges (the little bones) on the other fingers of your hand. You’ll find 12. That’s how the Babylonians and other ancient peoples counted. The system spread in the Middle-Age — from the calendar (12 months) to money (12 deniers in a sou - a sytem that continued in Brittain with 12 pennies in a shilling!).

And it stuck. Even today, we talk about dozens (douzaine in French) — of eggs, of snails (well, I should rather say escargots, right!), of oysters. An ancient habit that somehow survived the French Revolution and modern metric logic.

Eighty = Four Twenties?

French numbers get weirder after 60. You’ve got soixante-dix for 70, quatre-vingt for 80, and quatre-vingt-dix for 90. If you’re wondering why the French make you do math just to say your age, you’re not the only one.

In medieval France, people counted by twenties. This might have come even from a further-away time, probably from the Celts. So 40 was deux vingts, 60 was trois vingts, 80 was quatre vingts. Logical… in a very old-school way. In the 17th century, dictionary makers chose to keep the mix: trente, quarante, cinquante, soixante — then back to quatre-vingt. Why? Some say it helped with mental math. Others say it was just tradition. Whatever the reason, the math survived.

In some parts of the French-speaking world (la francophonie), people say septante or nonante, based on the decimal system. Like in Belgium or Switzerland. I like this so much! Unfortunately, if you say that in France, people will not always understand you (true story!).

Languages Keep Traces of the Past

French numbers aren’t random. They’re traces of the past, still alive in everyday language. When you say une demi-douzaine d’œufs, you’re speaking like a medieval merchant. When you say quatre-vingt, you’re echoing a Celtic rhythm of counting by twenties.

As a language learner, this can feel frustrating. Why not just use huitante? Or why not always count by tens? But there’s something beautiful here, too. Each irregularity tells a story. French doesn’t just teach you how to say numbers — it tells you where those numbers came from.

Want to Understand More?

I love stories like this. When I studied English at university, discovering the International Phonetic Alphabet was a revelation. It felt like finding a secret code hidden in the language. French numbers are the same: behind them, there’s a whole logic waiting to be explored.

Want to go deeper into the sounds, structures, and stories of French? Write to me at contact@clemenceparis.fr or chat with me on Facebook. Let’s explore the language together — and maybe do a bit of time travel on the way.