France had a calendar with 10-hour days during the revolution.

  • 10-hour decimal clock
10-hour decimal clock
Michael Wheatley/ Alamy Stock Photo

French Revolutionary Time was a short-lived concept that used a base-10 timekeeping system. Otherwise known as “decimal time,” this unprecedented method included 10-hour days, 100 minutes per hour, and 100 seconds per minute. Each day was divided into 10 equal parts, with “zero” marking the start (what is now midnight) and “five” denoting the midpoint (noon). This meant that every hour was more than twice as long as an hour of standard time. New clocks and watches were even manufactured displaying both decimal time and standard time, to considerable confusion. 

While France formally adopted this practice on November 24, 1793, the idea was first promoted in 1754. That year, mathematician Jean le Rond d’Alembert drew inspiration from the base-10 numeral system that had existed since ancient times and argued that it would be easier and more convenient to calculate times that were divisible by 10. The concept was revived in 1788 and met with enthusiasm from French revolutionaries seeking to shed their ties to the past. French Revolutionary Time was later adopted by the French Parliament, though it proved to be unpopular among citizens who found the switch confusing. The new system was deemed optional on April 7, 1795, and the country ultimately reverted to the previous timekeeping method.

In addition to changing how the country kept time, revolutionary France also adopted the French Republican calendar. The new formula divided the year into 12 months, each of which contained three 10-day weeks. To bring the total days up to 365, France tacked on five additional days at the end of the year as holidays. Debuted on October 24, 1793, the new calendar was also short-lived, and was abolished by Napoleon Bonaparte on January 1, 1806.

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