Hour (H) Conversions
An hour (symbol: h) is a unit of time usually equal 60 minutes. The time of day is typically expressed in English in terms of hours. Whole hours on a 12-hour clock are expressed using the contracted phrase o'clock, from the older of clock. In metric system, hours are an accepted unit of time defined as 3,600 atomic seconds.
All Hour Converters
The metric system bases its measurements of time upon the second, defined since 1952 in terms of the Earth's rotation in AD 1900. Its hours are a secondary unit computed as precisely 3,600 seconds. However, an hour of Coordinated Universal Time (UTC), used as the basis of most civil time, has lasted 3,601 seconds 27 times since 1972 in order to keep it within 0.9 seconds of universal time, which is based on measurements of the mean solar day at 0° longitude.