| Planck Time | tP | Planck time is the time it would take a photon travelling at the speed of light to cross a distance equal to the Planck length. |
| Quectosecond | qs | A quectosecond is an SI unit of time equal to 10^-45 of a second. |
| Rontosecond | rs | A rontosecond is an SI unit of time equal to 10^-27 of a second. |
| Yoctosecond | ys | A yoctosecond is an SI unit of time equal to 10^-24 of a second. |
| Zeptosecond | zs | A zeptosecond is an SI unit of time equal to 10^-21 of a second. |
| Attosecond | as | An attosecond is an SI unit of time equal to 10^-18 of a second. |
| Femtosecond | fs | A femtosecond is an SI unit of time equal to 10^-15 of a second. |
| Picosecond | ps | A picosecond is an SI unit of time equal to one trillionth of a second. |
| Nanosecond | ns | A nanosecond is an SI unit of time equal to one billionth of a second. |
| Microsecond | μs | A microsecond is an SI unit of time equal to one millionth of a second. |
| Millisecond | ms | A millisecond is an SI unit of time equal to one thousandth of a second. |
| Second | s | The second is the base unit of time in the International System of Units (SI). It is qualitatively defined as the second division of the hour by sixty, the first division by sixty being the minute. |
| Minute | min | The minute is a unit of time equal to 60 seconds, or 1/60th of an hour. |
| Hour | h | The hour is a unit of time conventionally reckoned as 1⁄24 of a day and scientifically reckoned as 3,599–3,601 seconds, depending on conditions. |
| Day | d | The day is a unit of time. In common usage, it is an interval equal to 24 hours. |
| Week | wk | A week is a time unit equal to seven days. |
| Month | mo | A month is a unit of time, used with calendars, which is approximately as long as some natural period related to the motion of the Moon; month and Moon are cognates. |
| Year | yr | A year is the orbital period of a planetary body, for example, the Earth, moving in its orbit around the Sun. |
| Decade | dec | A decade is a period of 10 years. |
| Century | c | A century is a period of 100 years. |
| Millennium | m | A millennium is a period of 1000 years. |
| Age of the Universe | U | The age of the universe is the time elapsed since the Big Bang. |
