The hour is a unit of measurement of time. in modern usage, an hour comprises 60 minutes, or 3,600 seconds. it is approximately 1/24 of a mean solar day. an hour in the universal coordinated time (utc) time standard can include a negative or positive leap second, and may therefore have a duration of 3,599 or 3,601 seconds for adjustment purposes. although it is not a standard defined by the international system of units, the hour is a unit accepted for use with si, represented by the symbol h.