Unit of time

A **unit of time** or **midst unit** is any particular time interval, used as a standard way of measuring or expressing duration. The base unit of time in the International System of Units (SI) and by extension most of the Western world, is the second, defined as about 9 billion oscillations of the caesium atom.

Note: The light-year is not a unit of time, but a unit of length of about 9.5 petametres (9 454 254 955 488 kilometers).

## List

|scope="col"|Unit|scope="col"|Length, Duration and Size|scope="col"|Notes|
| --- | --- | --- | --- | --- | --- |
|Planck time||The amount of time light takes to travel one Planck length.||||
|yoctosecond||One septillionth of a second.||||
|jiffy (physics)||The amount of time light takes to travel one fermi (about the size of a nucleon) in a vacuum.||||
|zeptosecond||One sextillionth of a second. Time measurement scale of the NIST strontium atomic clock. Smallest fragment of time currently measurable is 247 zeptoseconds.||||
|attosecond||One quintillionth of a second.||||
|femtosecond||One quadrillionth of a second. Pulse time on fastest lasers.||||
|svedberg||Time unit used for sedimentation rates (usually of proteins).||||
|picosecond||One trillionth of a second.||||
|nanosecond||One billionth of a second. Time for molecules to fluoresce.||||
|shake||10 nanoseconds, also a casual term for a short period of time.||||
|microsecond||One millionth of a second. Symbol is µs||||
|centimillisecond||One hundred thousandth of a second or one hundredth of a millisecond.||||
|decimillisecond||One ten-thousandth of a second or one tenth of a millisecond.||||
|millisecond||One thousandth of a second. Shortest time unit used on stopwatches.||||
|centisecond||One hundredth of a second.||||
|jiffy (electronics)|or|Used to measure the time between alternating power cycles. Also a casual term for a short period of time.||||
|decisecond||One tenth of a second.||||
|quadrisecond / semisemisecond||One quarter of a second.||||
|semisecond / half second||One half of a second.||||
|second||SI Base unit.||||
|decasecond||||||
|half a minute||It’s known by math.||||
|minute||||||
|milliday||Also marketed as a ".beat" by the Swatch corporation; Milliday is a more accurate name.||||
|moment|( on average)|Medieval unit of time used by astronomers to compute astronomical movements, length varies with the season.||||
|hectosecond||1 minute and 40 seconds||||
|ke||14 minutes and 24 seconds||||
|kilosecond||16 minutes and 40 seconds||||
|half an hour||It’s known by math.||||
|hour||||||
|decakilosecond||Ten thousand seconds or ten kiloseconds.||||
|Half an day||Its known by math.||||
|day||Longest unit used on stopwatches and countdowns.||||
|hectokilosecond||One hundred thousand seconds or one hundred kiloseconds.||||
|week||Also called "sennight".||||
|megasecond||277.777778333333 hours or about 1 week and 4.6 days.||||
|fortnight||14 days||||
|lunar month||Various definitions of _lunar month_ exist.||||
|month|28-31 days|Occasionally calculated as 30 days.||||
|quarter and season||||||
|quadrimester||||||
|semester||A division of the academic year. Literally "six months", also used in this sense.||||
|half year||||||
|lunar year||||||
|year||||||
|common year||52 weeks and 1 day.||||
|tropical year||Average.||||
|Gregorian year||Average.||||
|sidereal year||||||
|leap year||and||||
|biennium||||||
|triennium||||||
|quadrennium||||||
|olympiad||||||
|lustrum||||||
|decade||||||
|indiction||||||
|gigasecond||16,666,666.6667 minutes or about 31.7 years.||||
|jubilee||||||
|century||||||
|millennium||Also called "kiloannum".||||
|terasecond||About 31,709 years.||||
|megaannum||Also called "Megayear." 1,000 millennia (plural of millennium), or 1 million years.||||
|petasecond||About 31,709,791 years.||||
|galactic year||The amount of time it takes the Solar System to orbit the center of the Milky Way Galaxy one time. Around 230,000,000 years.||||
|cosmological decade|varies|<small>10 times the length of the previous cosmological decade, with CÐ 1 beginning either 10 seconds or 10 years after the Big Bang, depending on the definition.</small>||||
|gigaannum||Also refers to an indefinite period of time, otherwise is 1,000,000,000 years.||||
|exasecond||About 31,709,791,983 years.||||
|zettasecond||About 31,709,791,983,764 years.||||
|yottasecond||About 31,709,791,983,764,584 years.||||
|Age of universe|13700000000years|Roughly 4.35 yottaseconds||||