This site examines decimal time, which is the measure of time using units related by powers of ten. This includes decimal time of day, decimal dates, the history of decimal time and various decimal time proposals. This site also examines calendars, Star Trek's stardates, and provides conversions to and from different formats of decimal time, links to other decimal time web sites, as well as the blog.

Decimal vs. Standard Time

Our current civil time is based mostly on the numbers "12" and "60", dating back to the duodecimal and sexagesimal systems used by the ancient Babylonians, instead of the decimal systems of time used in China. Although the whole world now uses decimal metric units for almost every other quantity, we still use hours and minutes instead of metric time units such as kiloseconds or megaseconds, and we still divide days into 2 halves by 12 hours by 60 minutes by 60 seconds, and multiply them with weeks of 7 days, months of 30 or 31 days (or 28 or 29) and years of 12 months. It is difficult to make time calculations involving standard units, which is why scientists and computer programmers convert dates and times to decimal time units.

Types of Decimal Time

  • French Revolutionary Time divided the day into ten hours, each hour into 100 decimal minutes, each minute into 100 decimal seconds, with ten-day weeks, introduced in France in 1793
  • Fractional days are decimal times of day expressed as a decimal fraction, obtained by dividing the number of hours by 24, which are added to decimal dates and other dates by astronomers and computer programmers
  • Swatch Internet Time is a proprietary decimal time standard from the Swiss watch company which counts 0.001 fractions of a day, called ".beats"
  • Decimal dates count the decimal number of whole and fractional days since a specific epoch; examples include Julian Dates and Excel serial dates
  • Unix Time is a count of seconds from January 1, 1970, used by Unix and other computer systems