How to use the units of time list
- Find a unit by name (nanosecond) or symbol (ns), or pick shorter or longer than a second.
- Read how many seconds it is, written as a power of ten for the tiny ones.
- Use the light column for a feel of the scale: light covers about 30 cm in a nanosecond.
The metric pattern
Below a second, time units use the metric prefixes, each step a thousand times smaller:
| Unit | Fraction of a second |
|---|---|
| millisecond (ms) | 1 / 1,000 |
| microsecond (µs) | 1 / 1,000,000 |
| nanosecond (ns) | 1 / 1,000,000,000 |
| picosecond (ps) | 1 / 1,000,000,000,000 |
Above a second, the units are the old ones: 60 seconds in a minute, 60 minutes in an hour and 24 hours in a day, a system that goes back to ancient Egypt and Babylon.
Where you meet them
Milliseconds come up in reaction times and network ping, microseconds and nanoseconds in computer timing, and femtoseconds in laser physics. To add up hours and minutes, use the time duration calculator; to read computer timestamps, the Unix timestamp converter. For the prefixes themselves, see the metric prefixes chart.