Hour (h)
Definition
The hour (symbol h) is a unit of time equal to exactly 3,600 seconds, or 60 minutes. It is one of the non-SI units accepted for use with the International System of Units and is the primary unit for daily scheduling and workweek measurement.
History
The 24-hour day comes from ancient Egyptian astronomy, which divided daylight into 12 parts and night into another 12. Equal hours of fixed length appeared with the spread of mechanical clocks in Europe from the 13th and 14th centuries; before that, the length of an hour varied with the seasons.
Modern time zones, established at the International Meridian Conference in 1884, standardized civil time worldwide in increments of one hour relative to Coordinated Universal Time. Today the hour is defined exactly as 3,600 SI seconds.
Standard reference
Defined as 3,600 seconds exactly. Accepted for use with the SI under the BIPM SI Brochure (Table 8). Civil time zones are defined as fixed UTC offsets in whole hours under ITU-R TF.460.
Common conversions
| 1 h | = 60 min |
|---|---|
| = 3,600 s | |
| = 0.0416667 d |