Second (s)
The second (s) is the SI base unit of time, defined by fixing the caesium-133 hyperfine transition frequency at exactly 9 192 631 770 Hz.
Symbol: s
Quantity: time (duration)
SI relation: s is the coherent SI unit of time.
Derivation: SI base unit: 9 192 631 770 periods of the caesium-133 hyperfine transition
Exact: yes, by definition
History
The atomic definition was adopted in 1967, replacing the second defined as a fraction of the mean solar day and later of the tropical year.
Typical uses
- Every derived SI unit that involves time (m/s, Pa·s, W = J/s)
- Process timing, exposure and dwell times
- Flow totals (volume per second)
Convert seconds to other units
| Conversion | 1 s equals | Reverse |
|---|---|---|
| second to minute | 0.01666666667 min | minute to second |
| second to hour | 0.0002777777778 h | hour to second |
| second to millisecond | 1000 ms | millisecond to second |
| second to day | 0.00001157407407 d | day to second |
Open the Time Converter to convert any value between all units.
Sources
- The International System of Units (SI), 9th edition (SI Brochure), Bureau International des Poids et Mesures , Section 2.3.1, base unit definitions.
Last reviewed: . Factors are stored exactly and computed with 50-digit decimal arithmetic. See how we verify conversion factors.
Cite this page
APA
Scientific Converters. (2026, October 15). Second (s). Retrieved October 17, 2026, from https://scientificconverters.com/units/second/
IEEE
Scientific Converters, "Second (s)," scientificconverters.com. Accessed: Oct. 17, 2026. [Online]. Available: https://scientificconverters.com/units/second/