Decimal Time: How the French Made a 10-Hour Day
by Chris Higgins / January 6, 2013

“Everybody knows that there are 24 hours in a day, 60 minutes in an hour, and 60 seconds in minute.* But in 1793, the French smashed the old clock in favor of French Revolutionary Time: a 10-hour day, with 100 minutes per hour, and 100 seconds per minute. This thoroughly modern system had a few practical benefits, chief among them being a simplified way to do time-related math: if we want to know when a day is 70% complete, decimal time simply says “at the end of the seventh hour,” whereas standard time requires us to say “at 16 hours, 48 minutes.” French Revolutionary Time was a more elegant solution to that math problem. The trick was that every living person already had a well-established way to tell time, and old habits die hard. French Revolutionary Time officially began on November 24, 1793 although conceptual work around the system had been going on since the 1750s. The French manufactured clocks and watches showing both decimal time and standard time on their faces (allowing for conversion and confusion). These clock faces were spectacularly weird. Here’s one — see if you can figure out when primetime TV starts:

The system proved unpopular. People were unfamiliar with switching systems of time, and there were few practical reasons for non-mathematicians to change how they told time. (The same could not be said of the metric system of weights and measurements, which helped to standardize commerce; weights and measurements often differed in neighboring countries, but clocks generally did not.) Furthermore, replacing every clock and watch in the country was a spendy proposition. The French officially stopped using decimal time after just 17 months — French Revolutionary Time became non-mandatory starting on April 7, 1795. This didn’t stop some areas of the country from continuing to observe decimal time, and a few decimal clocks remained in use for years afterwards, presumably leading to many missed appointments. The French tried again in 1897, when the Commission de décimalisation du temps proposed a 24-hour day with 100-minute hours, again with 100 seconds per minute. This proposal was scrapped in 1900. … The French Republican Calendar was another attempt by revolutionary France to decimalize everything. It wasn’t particularly successful. Also interesting is the Chinese ke, a unit of decimal time.”

The French Republican Wall Calendar

“In 1793 French revolutionaries rejected the Gregorian calendar and introduced a new calendar in which weeks had 10 days, months were named for the weather and every day of the year was designated in honor of a plant, tool or animal. Highlights included days named for Celery, Goose, Hammer, Radish and Carp. Known as the French Republican Calendar, citizens were compelled to use the calendar under pain of death, but it was so stupid that everyone decided it was worth the risk not to.

In 2015, Ursula published a wall calendar version of the French Republican Calendar despite the fact that it was never meant for this purpose. You can learn more about this extremely dumb, yet totally charming, folly below or, if reading is too hard, you can watch Ursula explain it to a room full of drunk people here.

An Introduction to the French Republican Calendar

“On the morning of October 24th, 1793, the citoyens of the recently established French Republic — aristocrats and peasants alike — awoke to find that time had changed. It wasn’t October 24th at all. It was the Celery Day of Brumaire, in Year Two of the French Era. If they were waking up at 6 AM, say to get a head start on rioting over bread, to show up for an early execution, or to just go to their usual job doing the same physical drudgery they’d been doing before the Revolution, it wasn’t actually 6 AM. It was 3:60.

We’ve all committed to memory a history class reduction of the highlights of the French Revolution. The aristocracy was overthrown, the church was banned, people were beheaded. Sans-culottes, check. Marie Antoinette, check check. The Fourth Estate, check check check. But somewhere in that narrative the massive extent of the social and cultural transformation in late 18th-century France gets lost. The new order sought to eliminate any remaining trace of the Ancien Régime, and central to these efforts was the implementation of a new calendar and a totally overhauled system of time measurements. You know, just the most basic categories we organize our lives around. It’s hard to imagine the Gregorian calendar (the one we use today) seeming anything but innocuous — but to a bunch of very excitable revolutionaries in 1791 it was très réactionnaire.

Months named after ancient gods smacked of superstition and paganism. Days of the week were structured around religious practice and, making matters worse, the Church devoted every day of the year to a specific saint. Moreover, French radicals, newly enamored of the metric system, found the whole 24/7/365 thing deeply unappealing. In short, the old system of measuring days and counting hours flew in the face of Enlightenment rationality — a central pillar of revolutionary ideology. In other words, reason was the new reason for the season, so the seasons had to be changed.

In 1792, a commission made up of a couple mathematicians, a naval geographer, two astronomers, a horticulturalist, a poet, and a handful of politicians was convened and got to work developing a new, revolutionary calendar.(1) Months were the first to go. There were still 12, and they were still divided into four seasons organized around solstices, but that’s where the similarity stops. Each month was renamed to reflect the climatological conditions of the time of year in which it occurred. The first month of the year was dubbed Vendémiaire (Grape Harvest): it began on the autumn equinox, on or around the 22nd of September on the Gregorian calendar. It was followed by Brumaire (Foggy), Frimaire (Frosty), Nivôse (Snowy), Pluviôse (Rainy), Ventôse (Windy), Germinal (Germination), Floréal (Flowering), Prairial (Meadow), Messidor (Harvest), Thermidor (Hot), and Fructidor (Fruit). Rather than saints, each day was designated in honor of a specific animal, plant, or tool important to French society. Given that there were 12 months of 30 days each, 360 individual days were ultimately named. For example, the seventh day of the Frosty month was Cauliflower. The fifth day of the Windy month was Goat. You could celebrate rhubarb on the 11th day of the Flowering month, artichokes on the 12th day of the Harvest month, and pitchforks on the 20th day of the Meadow month. There were days named for oats, hops, cows, cats, pheasants, trout, apples, jasmine, peas, onions, garlic, baskets, verbena, you name it. Even carp. The lowly carp got its very own day. You just probably couldn’t remember when it was.

Of course there’s a problem inherent in having twelve 30-day months: the five days (or six in a leap year) you have left over. The solution devised by the calendar’s designers was an intercalary period between the end of the year on the 30th (or “Basket”) of Fructidor and the first (or “Grapes”) of Vendémiaire. This period was to be known as the sans-culottides — though not because it was pants-optional or even business casual. These “complementary days” were named for the radical urban working class without whom the Revolution would never have happened. Accordingly, each day was named for a romantic aspect of this class — virtue, labor, genius, honor, conviction, and in leap years, revolution. Appropriately, workers were to be given these days off. Which was nice, considering that under the new calendar, everyone had far less free time than they had prior to the Revolution (one day of rest for every nine days worked as opposed to one day out of seven, aka Sunday). To paraphrase Robespierre, “Hey sans-culottes, just our little way of saying merci!” The last day of the sans-culottides was New Year’s Eve, which took place months earlier than the customary December 31.  So, every year while the rest of the Western world was winding its way through September, the French started the year anew. Rejecting the Gregorian calendar meant resetting the march of history to zero — quite literally. 1792 became year 1 in the first century of the French Era. I am writing this in the 224th year of the third century of the French Era, for what it’s worth.

But the renaming of months and days and the renumbering of years was just the icing on the crazy let-them-eat-cake. The real problem lay with the newly imposed system of decimal time. Each month had 30 days grouped into three 10-day weeks (known as “decades”), and days of the week were renamed to reflect this (Primidi was first day, Duodi was second day, Tridi was third day, etc.). No one was expected to know the particular animal / mineral / vegetable / tool corresponding to each day (so it was okay if you weren’t aware that it was, say, Beet Day) but you probably should have known that it was the 4th of Brumaire. One slight advantage to this approach was that every year the same day of the month fell on the same day of the week (so 4 Brumaire always fell on a Quartidi, since it’s the fourth day). This might have made things a little easier and also meant that, had they existed, you would never have needed to replace a wall calendar. The reorganization of time followed a similar logic. Days were 10 hours long and each hour comprised 100 minutes. A minute lasted 100 seconds. This might sound like a nifty, organized means of charting time. It’s not. The new system actually modified the fundamental length of a second, which is, of course, ultimately based on the amount of time it takes for the earth to revolve around the sun. Seconds got shorter precisely because hours got longer. Having 10 hours in a day, each clocking in at a hundred 100-second minutes, meant that an hour took about 145 “normal” minutes while a second was just .864 times the length of a conventional second. In theory, if the rest of the world got on board and started measuring time this way, it might work. But they didn’t and it doesn’t, dooming the calendar to being perpetually out of sync with everyone else. Not to mention it’s a tricky way to tell time. New clocks were manufactured to display decimal time, but weirdly, did not sell well.

As you can see, my version of French Republican (Wall) Calendar in no way resembles its original renderings. Major artistic license has been taken in this project. The point of this calendar — The French Republican (Wall) Calendar — is not to keep track of the dates, but to appreciate the specific items designated for every day of the year, and to see them presented visually. The authors of the original calendar thought carefully about when to honor each item. If they did it right, this version should at least be somewhat predictive of what will come into season when. For example, rhubarb almost always appears in the grocery store within a week of Rhubarb Day. Tulips, violets, and lilacs also tend to appear in sync. And for those of us living in northern climes, there is something truly appropriate about assigning coal, peat, and manure (yes, manure) to the depths of January. Finally, it is precisely the specificity and breadth of the items that, I believe, makes this calendar so unique and evocative. The original calendar was never meant for one’s wall, but this one is. Put it up. Contemplate carrots on Carrot Day. Note that what English-speakers call lungwort, the French call pulmonaire. Tell your cat it’s Cat Day. Take yourself out for a beer on Hops Day, a glass of wine on Grape Day, and a gin and tonic on Juniper Day. Just take a moment, every day, to appreciate all of these things that are as common in 2016 as they were in 1792 (okay, it’s a been awhile since you’ve seen someone play the shawm, I get that). It’s as close to a sort of spiritual gratitude us secular, latter-day républicains may ever achieve.”

1. “Notably, less than half of the participants were eventually executed, which, if not exactly a testament to the strength of their endeavor, certainly suggests it was a better gig than, say, neighborhood captain in the Committee of Public Safety.

2. For a more scholarly (read: more accurate) understanding of the calendar, the following books are highly recommended: Time and the French Revolution: The Republican Calendar 1789-Year XIV by Matthew Shaw and The Calendar in Revolutionary France: Perceptions of Time in Literature, Culture and Politics by Sanja Perovic.”

Relics of Decimal Time from 1793-1795

“The collection of scientific instruments at the Musée des Arts et Métiers in Paris, France includes a few decimal clocks and pocketwatches. When filming the kilogram and meter standards, I learned about decimal time from Dr. Lalande, who is a curator of scientific instruments at the Musée. His section includes some decimal clocks made in the 1790s. Some of the timepieces show 10 hours and their subdivisions only; others also include duodecimal time markings. During the French Revolution, the desire to convert all measurement systems to base 10 included changing the way time was named, managed and measured.

Since the 1750s, prominent French mathematicians and other scholars had discussed the benefits of decimalized calculations, and in 1793, Jean-Charles de Borda officially proposed decimal divisions for days and hours: 10 hours of 100 minutes. Each minute had 100 seconds (about 14% shorter than traditional seconds). The calendar would keep 365 days (or 366 in leap years) but the 12 months would be of uniform duration, all having 30 days. These months were given new names that celebrated the seasons and farming, for example, fructidor was the third of the summer group of months (who suffixes were -dor) and named after fruit. Months were divided into 3 décades of 10 days, and the tenth day, called décadi, replaced Sunday as a day of rest. The remaining five or six days became holidays, not commemorating saints or kings, but activities considered to further humankind and the nation, such as virtue, labor and the Revolution itself.

While decimal-based weights, measures, and currency were eventually adopted in France, decimal time and the French Republican calendar failed. In September 1805, Napolean Bonaparte declared that in 1806 France would resume using the Gregorian calendar. Several scholars point to his desire to reconcile with the Church, as the Revolutionaries had used the 10-day “week” to divert attention away from traditional Sunday activities. The Republican calendar lasted about 12 years, but mandatory use of decimal time lasted only 197 days, from September 22, 1794 to April 7, 1795.

“Wearing a decimal timepiece was one hallmark of a “good citizen.”

Why? Decimal time was approved by the State (some towns installed decimal clocks that continued to run after the 10-hour day was no longer mandatory) and using the state-sanctioned measures was a sign of support. But unlike standardized weights and measures, or decimal currency, decimal time didn’t solve a widespread problem3. Beyond the inherent appeal of base-10 mathematics to decision-makers of the time, decimal time made it easier to know exactly how much of the day had passed. But these two advantages weren’t enough to justify the hassle of new notation and the expense of new mechanical devices. Though official, decimal time was used only by a few people for specialized areas, notably the mathematician Jean-Pierre Laplace.”


  1. Shaw, Matthew. Time and the French Revolution: The Republican Calendar, 1789-Year XIV, 2011. 45.
  2. Yvan Pointurier. includes a close-up photo with the caption: “Precision watch with decimal seconds, Robert Robin, 1793.”
  3. Vera, Hector. Decimal Time: Misadventures of a Revolutionary Idea, 1793–2008. KronoScope 9.1–2 (2009) 29–48.
  4. Doyle, William. The Oxford History of the French Revolution, 2003. Ch. 12.
  5. Marciano, John Bemelmans. Whatever Happened to the Metric System?: How America Kept Its Feet. 2014. Ch. 5.
  6. Andrew, George Gordon. Making the Revolutionary Calendar. The American Historical Review, Vol. 36, No. 3 (April 1931), pp. 515-532.