General Data > Units of Time
The table below shows units and values for various periods of time.
The SI base unit for time is the 'second'. Larger units such as 'hour' and 'day' are derived from the second.
Common Units of Time
| Unit |
Size |
Notes |
| Femtosecond |
10−15 second |
|
| Picosecond |
10−12 second |
|
| Nanosecond |
10−9 second |
|
| Microsecond |
10−6 second |
|
| Millisecond |
1/1,000 second |
|
| Second |
SI base unit |
|
| Minute |
60 seconds |
|
| Hour |
60 minutes |
|
| Day |
24 hours |
|
| Week, Sennight |
7 days |
|
| Fortnight |
14 days; 2 weeks |
|
| Month |
28 to 31 days |
|
| Quarter |
3 months |
|
| Year |
12 months |
|
| Tropical year |
365.24219 days |
Average |
| Olympiad |
4 years |
|
| Lustrum |
5 years |
obsolete |
| Decade |
10 years |
|
| Indict |
15 years |
obsolete |
| Score |
20 years |
|
| Generation |
25 years |
approximate |
| Century |
100 years |
|
| Millennium |
1,000 years |
|