How many seconds are there in an hour?

An hour is a unit of time conventionally reckoned as 1⁄24 of a day and scientifically reckoned between 3,599 and 3,601 seconds, depending on the speed of Earth's rotation. There are 60 minutes in an hour, and 24 hours in a day.

The hour was initially established in the ancient Near East as a variable measure of 1⁄12 of the night or daytime. Such seasonal, temporal, or unequal hours varied by season and latitude.

Equal or equinoctial hours were taken as 1⁄24 of the day as measured from noon to noon; the minor seasonal variations of this unit were eventually smoothed by making it 1⁄24 of the mean solar day. Since this unit was not constant due to long term variations in the Earth's rotation, the hour was finally separated from the Earth's rotation and defined in terms of the atomic or physical second.