Why did revolutionary France try to replace the 24-hour day with decimal time?

Nature · Published 3 October 2026 Swipe more like this →

In short: During the French Revolution, officials attempted to overhaul time itself by dividing the day into ten decimal hours. This radical experiment aimed to simplify calculations by aligning time with the base-ten metric system. While it failed to replace our traditional clocks, the concept persists in science and digital computing today.

The French Republican calendar, introduced in 1793, sought to eliminate the 'arbitrary' division of the day into 24 hours, 60 minutes, and 60 seconds. By dividing the day into 10 decimal hours, each containing 100 decimal minutes and 100 decimal seconds, the system created a total of 100,000 decimal seconds per day. Proponents like Jean-Charles de Borda argued that this unified representation would make timestamps easier to convert and compute, as the units would share the same base as the decimal number system.

Despite the ambition, the system faced immense public resistance. Critics like C.A. Prieur argued that the change offered no practical advantage to the average citizen, while the cost of replacing clocks and the force of habit made adoption impossible. Mandatory use was suspended in 1795, though some cities continued using decimal clocks for years. The transition was further complicated by competing proposals, such as Joseph-Louis Lagrange’s suggestion to use 'decidays' and 'centidays' to represent time as simple two-digit values.

While the public rejected decimal time, it found a permanent home in specialized fields. Astronomers continue to use fractional days for precision, and the concept influenced modern digital timekeeping. In 1998, Swatch introduced 'Internet Time,' dividing the day into 1,000 '.beats.' Each beat equals 86.4 standard seconds, and extended versions of this system mirror the French decimal structure. Today, decimal time remains a testament to the revolutionary desire to impose rational, mathematical order on the natural world.

General information, not professional advice. Spotted an error? Flag the card or see corrections and complaints.

Intellect Plus is a visual educational discovery platform for exploring fascinating facts and ideas. Brain Food, Not Brain Rot. What is Intellect Plus?

Related

• Why the French Revolution tried to replace the week with a ten-day cycle
• Why the world abandoned the 12-hour clock for a global standard
• How the French Revolution replaced chaotic medieval measurements with a universal, natural standard.
• The metric system was born from a revolutionary quest that ended in scientific error
• Why is our day divided into twenty-four hours of sixty minutes each?
• Shakespeare's desert of Bohemia had no sand, only an absence of people
• Fair-weather cumulus clouds are powered by the heat of their own condensation
• In Israel's Negev, dew supplies nearly half the water of some desert shrubs
• An average thunderhead weighs about half a million kilograms
• A downburst is a violent, localized column of sinking air that mimics tornado damage
• Why the hidden geometry of atoms dictates the physical world around us
• Nearly half of all the world's land drains into the Atlantic Ocean

More in Earth science · More in Nature · Latest · A–Z · All topics