# Time unit conversion table

This table contains conversions between almost all time units. Some units of time are common and some are relatively rare. This is a good query tool.  Time Converter

Name of unitSymbolDefinitionRelation to SI units
Atomic unit of timeaua0/( α · c )2.418 884254×10 −17 s
Callippic cycle ≡ 441 mo (hollow) + 499 mo (full) = 76 a of 365.25 d= 2.396 736 Gsor 2.398 3776 Gs
Centuryc≡ 100 years (100 a)3.155 6952 Gs
Dayd= 24 h = 1440min= 86.4 ks
Day (sidereal)d≡ Time needed for the Earth to rotate once around its axis, determined from successive transits of a very distant astronomical object across an observer's meridian ( International Celestial Reference Frame)86.1641 ks
Decadedec≡ 10 years (10 a)= 315.569 520 Ms
Fortnightfn≡ 2 wk= 1.2096 Ms
Helek≡ ​ 11080h= 3. 3s
Hipparchic cycle ≡ 4 Callippic cycles - 1 d= 9.593 424 Gs
Hourh≡ 60 min= 3.6 ks
Jiffyj≡ ​ 160s= 16. 6ms
Jiffy (alternative)ja≡ ​ 1100s= 10 ms
Ke(quarter of an hour) ≡ ​ 14h = ​ 196d = 15 min= 900 s
Ke (traditional) ≡ ​ 1100d = 14.4 min= 864 s
Lustre; Lustrum ≡ 5 a of 365 d = 157.68 Ms
Metonic cycle; enneadecaeteris ≡ 110 mo (hollow) + 125 mo (full) = 6940 d ≈ 19 a= 599.616 Ms
Millennium 1000years ( 1000 a)31.556 952 Gs
Millidaymd≡ ​ 11000d= 86.4 s
Minutemin≡ 60 s, due to leap secondssometimes 59 s or 61 s,= 60 s
Moment ≡ 90 s= 90 s
Month(full)mo≡ 30 d = 2.592 ×10 6 s
Month (Greg. av.)mo= 30.436 875 d2.6297 Ms
Month (hollow)mo≡ 29 d = 2.5056 Ms
Month ( synodic)moCycle time of moon phases ≈ 29.530 589 d(average)2.551 Ms
Octaeteris = 48 mo (full) + 48 mo (hollow) + 3 mo (full) = 8 a of 365.25 d = 2922 d= 252.4608 Ms
Planck time ≡ (​ Gc5) 121.351 211868×10 −43 s
SecondsTime of 9 192631770periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom at 0 K (but other seconds are sometimes used in astronomy). Also that time it takes for light to travel a distance of 299 792458metres.( SI base unit)
Shake ≡ 10 −8s= 10 ns
Sigma ≡ 10 −6s= 1 μs
Sothic cycle 1461a of 365 d= 460.740 96 Ts
SvedbergS≡ 10 −13s= 100 fs
Weekwk≡ 7 d = 168 h = 10 080 min= 604.8 ks
Year(common)a, y, oryr365 d= 31.536 Ms
Year (Gregorian)a, y, oryr= 365.2425 d average, calculated from common years (365 d) plus leap years (366 d) on most years divisible by 4. See leap yearfor details.= 31.556 952 Ms
Year (Julian)a, y, oryr= 365.25 d average, calculated from common years (365 d) plus one leap year (366 d) every four years= 31.5576 Ms
Year (leap)a, y, oryr366 d= 31.6224 Ms
Year (mean tropical)a, y, oryrConceptually, the length of time it takes for the Sun to return to the same position in the cycle of seasons, [Converter 1]approximately 365.242 19d, each day being 86 400SI seconds 31.556 925 Ms
Year (sidereal)a, y, oryr≡ Time taken for Sun to return to the same position with respect to the stars of the celestial sphere, approximately 365.256 363 d31.558 1497632 Ms
Notes:
1. Jump up^see Callippic cyclefor explanation of the differences
2. ^ Jump up to:abcThis is based on the average Gregorian year. See above for definition of year lengths.
3. ^ Jump up to:abcdefghijklmnopWhere UTCis observed, the length of this unit may increase or decrease
depending on the number of leap secondswhich occur during the time interval in question.
4. Jump up^The length of ancient lustral cycles was not constant; see Lustrumfor more details