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Hour (h)

Also called: h, hr, hours

Definition: The hour is a unit of time equal to exactly 60 minutes or 3,600 seconds, and one 24th of a day. It is accepted for use with the SI but is not an SI unit itself.

Updated November 4, 2026 · How we check facts

The hour is a unit of time defined as 3,600 seconds, exactly, in NIST's conversion tables (3.6 × 10³ s). It equals 60 minutes, and 24 hours make one day of 86,400 s.

Formula

h = s ÷ 3,600

Example

A 40-hour work week is 40 × 3,600 = 144,000 s. A week has 7 × 24 = 168 hours (how many hours in a week). Convert with hours to minutes or hours to seconds.

Calculate it

Free toolHours Calculator (Timesheet)Add up a weekly timesheet, with overtime and pay.

Guides that explain it

Related terms

Minute (min)The minute is a unit of time equal to exactly 60 seconds, one 60th of an hour. It is accepted for use with the SI, and a day has 1,440 of them.Second (s)The second is the SI base unit of time, defined from the caesium-133 transition frequency of 9,192,631,770 Hz; there are exactly 60 seconds in a minute and 86,400 in a day.Gregorian CalendarThe Gregorian calendar is the civil calendar in worldwide use. Its 400-year cycle has 146,097 days, an average year of 365.2425 days, kept by the leap-year rule.Leap SecondA leap second is a one-second adjustment added to Coordinated Universal Time (UTC) so it stays within 0.9 s of Earth-rotation time, giving a day of 86,401 seconds.Leap YearA leap year has 366 days instead of 365. In the Gregorian calendar a year is a leap year if divisible by 4, except centurial years that are not divisible by 400.Sidereal DayA sidereal day is one rotation of the Earth relative to the stars: about 86,164.09 seconds, or 23 h 56 min 4.09 s, roughly 3 min 56 s shorter than a 24-hour solar day.Tropical YearThe tropical year is the time between successive spring equinoxes, about 365.2422 days (about 31,556,930 seconds). It is the natural year the Gregorian calendar approximates.

Sources

  1. NIST Guide to the SI (SP 811), Appendix B.8 — Factors for Units Listed Alphabetically
  2. NIST — SI Units: Time