**Full name:** hour

**Plural form:** hours

**Symbol:** hr

**Alternate spelling:** hrs

**Category type:** time

**Scale factor:** 3600

The SI base unit for time is the second.

1 second is equal to 0.00027777777777778 hours.

Valid units must be of the **time** type.

You can use this form to select from known units:

The hour was originally defined in Egypt as 1/24 of a day, based on their duo-decimal numbering system (which counted finger joints on each hand).

hours to Gaussian year

hours to tropical year

hours to lunar year

hours to century

hours to millennium

hours to second

hours to quarter

hours to millisecond

hours to sidereal month

hours to shake