Time units: overview and conversion factors
Second, minute, hour, day and week
The International System of Units (SI) defines the second as the base unit of time. Since 1967, the second has been exactly defined via the radiation of the caesium-133 atom: one second corresponds to 9,192,631,770 oscillation periods of this radiation. This definition enables atomic clocks with an accuracy of less than one second of deviation over millions of years – the foundation for GPS, mobile networks and global time synchronization.
The minute (60 seconds) and the hour (3,600 seconds) go back to the Babylonian sexagesimal system – a number system based on 60 that is over 4,000 years old. The number 60 is highly divisible (by 1, 2, 3, 4, 5, 6, 10, 12, 15, 20 and 30), which allows fractions without decimals. Via Greek and Arab astronomers, the system found its way into Western science and our time system today.
In everyday work, converting between minutes and hours is especially relevant: time tracking, project planning and billing by hourly rate often require converting decimal hours into hours and minutes. 1.5 hours equals 1 hour and 30 minutes, 0.25 hours equals 15 minutes. For sports timers, recipes or travel times, seconds, minutes and hours are used together depending on context – our calculator takes care of the conversion for you.
Days and weeks are calendar units that can also be derived from the second: 1 day = 86,400 seconds, 1 week = 604,800 seconds. In software development, logistics and project planning, time spans in days and weeks play a central role. Note: our calculator uses mean days (86,400 seconds) – leap seconds and daylight saving time changes are not taken into account, as these are irrelevant for most everyday applications.