Date and Time Calculators
Keep track of time & time zones with our Calculators & Converters for Time, Dates. The 12-hour notation is widely used in daily life, written communication, and is used in spoken language. The 24-hour notation is used in rare situations where there would be widespread ambiguity.
To measure time, we can use anything that repeats itself regularly. One example is the start of a new day (as Earth rotates on its axis). Two more are the phases of the moon (as it orbits the Earth), and the seasons of the year.
Even in ancient times, people developed calendars to keep track of the number of days in a year. They also developed sundials that used the moving shadows cast by the sun through the day to measure times smaller than a day. Today, highly accurate clocks can measure time in less than a billionth of a second.
The SI (International Systems of Units) unit of time is one second, written as s.