Room for ChanceWhat it measures and where it is used
Time intervals describe duration. The SI second is defined by a transition of caesium-133, replacing older astronomical definitions. Here a day means exactly 24 hours and a week seven such days. Months and calendar years are excluded because their lengths vary.
- Classification
- SI base quantity
- SI unit
- s
- Dimension
- T
L: length; M: mass; T: time; Θ: temperature; N: amount of substance. The dimension symbol N is not the unit symbol for newton.
How it works
The calculation first converts to a common reference unit, then to the destination unit. Factors in the table show the reference value for one unit.
Example
2 h ≈ 120 min
Available units
Reference unit: s
| Available units | Reference factor |
|---|---|
| s | 1 × x |
| ms | 0.001 × x |
| µs | 0.000001 × x |
| ns | 0.000000001 × x |
| min | 60 × x |
| h | 3,600 × x |
| d (24 h) | 86,400 × x |
| wk (7 d) | 604,800 × x |
Units, history and conventions
The International System of Units (SI) received its name in 1960. Since the 2019 revision, its definitions use fixed values of seven defining constants. SI base and derived quantities should not be confused with the different units used to express them.