Revolutionary calendar tool
Convert Gregorian dates into the calendar of the First Republic, switch back from Republican dates, and watch the day pass in decimal time.
Dates before 22 September 1792 have no Republican equivalent.
Thermidor 17, Year 234 (decade 2)
Thermidor · Decade 2 · Day 317
The French Republican calendar was introduced during the Revolution to replace royal, Christian, and Roman traces in everyday timekeeping with a rational civil system. Year 1 began on 22 September 1792, the day after the monarchy was abolished and close to the autumn equinox in Paris. The year was divided into twelve poetic months of thirty days, from Vendemiaire and Brumaire through Thermidor and Fructidor. Each month had three ten-day decades instead of seven-day weeks.
At the end of the twelve months came the sansculottides, five complementary festival days, or six in a leap year. This converter uses the proposed Romme rule: leap years are divisible by four except century years, unless divisible by 400. That makes the arithmetic clear and repeatable, though historical almanacs tied some early years to the observed Paris equinox.
Revolutionary reformers also tried decimal time: ten hours in a day, one hundred minutes in an hour, and one hundred seconds in a minute. It was elegant on paper but awkward for clocks, churches, markets, and habits. Napoleon abolished the Republican calendar from 1 January 1806, restoring Gregorian civil dates. The Paris Commune briefly revived Revolutionary dating in 1871, more as political symbolism than as a durable replacement for ordinary time.
The Republic never fully settled its own leap-year question. The founding decree tied New Year's Day to the autumn equinox as observed in Paris, and Years III, VII, and XI received their sixth complementary day on that basis. Gilbert Romme proposed replacing observation with fixed arithmetic, but the calendar was abolished before any rule was formally adopted. This tool applies the Romme rule throughout, so a converted date from the 1790s can land one day away from a printed almanac of the period. In exchange, every conversion is deterministic: the same input always returns the same output, which matters when you cite a date in writing.
Napoleon's coronation took place on 2 December 1804. Enter that date and the converter returns Frimaire 11, Year 13, matching the 11 Frimaire An XIII recorded in contemporary accounts, so the two reckonings agree for that year.
Now try 29 May 2026. The result is Prairial 10, Year 234, in the first decade of the month, with the Republican year having started on 22 September 2025. For this particular year the Paris equinox also fell on 22 September, so the two reckonings agree; the one-day gap described above only appears in years where the observed equinox misses the arithmetic start by a day.
A decimal day held 100,000 decimal seconds against the standard day's 86,400, so each decimal unit maps to a slightly odd standard value:
| Decimal unit | Standard equivalent |
|---|---|
| 1 decimal day (10 hours) | 24 hours |
| 1 decimal hour | 2 hours 24 minutes |
| 1 decimal minute | 1 minute 26.4 seconds |
| 1 decimal second | 0.864 standard seconds |
| Decimal 5:00:00 | 12:00 noon |
Year 1 began on 22 September 1792, the day after the monarchy was abolished. Under the Romme rule used here, Year 234 starts on 22 September 2025, so each Republican year straddles two Gregorian years.
They are the five festival days added after Fructidor to complete the 365-day year: Vertu, Genie, Travail, Opinion, and Recompenses. A leap year appends a sixth day, Revolution.
Under the Romme rule, years divisible by 4 are leap years unless they are century years not divisible by 400. Year 236 is a leap year with six sansculottides; Year 234 is not.
The calendar has no year zero and nothing before its epoch. Rather than invent a proleptic extension, the converter reports an error for any date before 22 September 1792.