**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 Julian year

hours to Julian month

hours to day

hours to anomalistic month

hours to quarter

hours to Gregorian month

hours to second

hours to fortnight

hours to millennium

hours to sidereal year