Decimal Time Converter: Convert Time in a Snap

What "decimal time" means here

This is French Revolutionary decimal time, not the "decimal hours" payroll conversion (e.g. 7:30 → 7.5 hours) that shares the name elsewhere. In this system a full day is split into 10 decimal hours instead of 24 standard hours, so each decimal hour runs 144 standard minutes long. It's the scheme France briefly mandated in 1794 before abandoning it — this tool reconstructs it for reference, not for scheduling.

Standard → decimal, worked example

12:00:00 noon is exactly halfway through the day: 43,200 seconds out of 86,400. Divide by 86,400 and multiply by 10 decimal hours: (43200 / 86400) × 10 = 5.0000000 decimal hours. That's why the default input of 12:00:00 converts to 5.0 — noon sits at the midpoint in both systems.

Decimal → standard, worked example

Going the other way, 5.0 decimal hours converts back to seconds using 8,640 seconds per decimal hour (86,400 ÷ 10): 5.0 × 8640 = 43,200 seconds, which formats as 12:00:00. A non-midpoint example: 2.5 decimal hours = 21,600 seconds = 06:00:00 standard time — a quarter of the way through the day.

Why 8,640 and not 3,600

In ordinary time, one hour is 3,600 seconds. In this decimal system, one decimal hour is 8,640 seconds because the day is divided into 10 units instead of 24. Reusing 3,600 here would silently produce the wrong answer — it's a common mistake when re-deriving this conversion by hand.