Hindu units of time

Hindu units of time are described in Hindu texts ranging from microseconds to trillions of years, including cycles of cosmic time that repeat general events in Hindu cosmology. Time is described as eternal. Various fragments of time are described in the Vedas, Manusmriti, Bhagavata Purana, Vishnu Purana, Mahabharata, Surya Siddhanta etc.

Sidereal metrics

Sidereal astrology maintains the alignment between signs and constellations via corrective systems of Hindu -origin known as ayanamsas, to allow for the observed precession of equinoxes, whereas tropical astrology ignores precession. This has caused the two systems, which were aligned around 2,000 years ago, to drift apart over the centuries.
Ayanamsa systems used in Hindu astrology include the Lahiriayanamsa and the Raman ayanamsa. The Fagan-Bradley ayanamsa is an example of an ayanamsa system used in Western sidereal astrology. As of 2020, zodiacal signs calculated using the Sri Yukteswar ayanamsa were around 23 degrees behind tropical zodiacal signs. Per these calculations, persons born between March 12 - April 12, for instance, would have the sun sign of Pisces. By contrast, persons born between March 21 - April 19 would have the sun sign of Aries per tropical calculations.
Sidereal Units:

Unit	Definition	Value in SI units
truti	base unit	≈ 308.6 ns
reṇu	60 truti	≈ 18.5 μs
lava	60 renu	≈ 1,111 μs
	60 lava	≈ 66.66 ms
	6	≈ 0.4 s
vipala	6	≈ 0.4 s
	10	≈ 4 s
pala	60 or 6	≈ 24 s
	60 or 6	≈ 24 s
	60 or 6	≈ 24 s
	60	≈ 1.44 ks
	60	≈ 1.44 ks
daṇḍa	60	≈ 1.44 ks
	2	≈ 2.88 ks
	60	≈ 86.4 ks
	30	≈ 86.4 ks

According to :

Unit	Definition	Value in SI units
truti	base unit	≈ 29.6 μs
tatpara	100 truti	≈ 2.96 ms
nimesha	30 tatpara	≈ 88.9 ms
	18 nimesha	≈ 1.6 s
	30	≈ 48 s
ghatika	30	≈ 1.44 ks
	2 ghatika	≈ 2.88 ks
	30	≈ 86.4 ks

Small units of time used in the Vedas:

Unit	Definition	Value in SI units
	base unit	≈ 26.3 μs
	2	≈ 52.67 μs
	3	≈ 158 μs
	3	≈ 474 μs
vedha	100	≈ 47.4 ms
lava	3 vedha	≈ 0.14 s
	3 lava	≈ 0.43 s
	3	≈ 1.28 s
	5	≈ 6.4 s
laghu	15	≈ 96 s
danda	15 laghu	≈ 1.44 ks
	2 danda	≈ 2.88 ks
	30	≈ 86.4 ks
masa	30	≈ 2,592 ks
ritu	2 masa	≈ 5,184 ks
ayana	3 ritu	≈ 15,552 ks
samvatsara	2 ayana	≈ 31,104 ks
of Deva	2 ayana	≈ 31,104 ks

Lunar metrics

The traditional lunar calendar system measures time based on the Moon's phases and its relation to the Sun. Unlike solar calendars, it uses units such as tithi, pakṣa, māsa, ṛitu, ayanam, and varsha to structure the year. This system was integral to ancient cultures for tracking time, planning festivals, and guiding agricultural practices. The following section provides an overview of these key time units and their relationships:

Unit	Definition	Equivalence
tithi	Time for 12° increase of longitudinal angle between Moon and Sun	≈ 1 day
paksha\|	15 tithis	≈ 15 days
	2 : gaura or during waxing moon; during waning moon	≈ 30 days
Ritu \|	2	≈ 60 days
ayanam	3	≈ 180 days
varsha	2 ayanams	≈ 360 days

Tropical metrics

Tropical metrics are time units used to measure intervals based on the tropical year and related cycles. This system includes units such as ghaṭi, yāma, and ahorātram. The following section explains these units and their approximate durations, offering insight into how time is organized in relation to the tropical year:

Unit	Definition	Equivalence
	base unit	≈ 24 minutes
	7.5	≈ 3 hours
	8	≈ 24 hours

Cosmic metrics

The table below contains calculations of cosmic Hindu units of time as experienced by different entities, namely humans, Pitris, Devas, Manu, and Brahma. Calculations use a traditional 360-day year and a standard 24-hour day for all entities.

Lifespans

define lifespans differently for humans, Pitris, Devas, Manus, and Brahma. The division of a year for each is twelve 30-day months or 360 days, where a day is divided into a 12-hour day proper and 12-hour night. A 30-day month amounts to four 7-day weeks with an extra 8th day every two weeks. A traditional human year is measured by the sun's northern and southern movements in the sky, where the new year commences only when the sun returns to the same starting point and a pause on the commencement otherwise. Ebenezer Burgess postulates an intercalary month was inserted every five years to anciently maintain the correspondence of the 360-day years with the true solar years. For this reason, a traditional 360-day year is equivalent to a modern ~365.24-day solar or tropical year.

Unit	Human	Pitri	Deva	Manu	Brahma
Brahma year	3,110,400,000,000 yr	103,680,000,000 yr	8,640,000,000 yr	~	1 yr
Manu year	3,067,200 yr	102,240 yr	8,520 yr	1 yr
Deva year	360 yr	12 yr	1 yr	~
Pitri year	30 yr	1 yr		~
Human year	1 yr			~

Cosmic date

According to Puranic sources, Krishna's departure marks the end of the human age of Dvapara-yuga and the start of Kali-yuga, which is dated to midnight on 17/18 February 3102BCE of the proleptic Julian calendar. We are currently halfway through Brahma's life, whose lifespan is equal to the duration of the manifested material elements, from which Brahma manifests his universe in kalpa cycles:

51st year of 100
1st month of 12
1st kalpa of 30
7th manvantara of 14
28th chatur-yuga of 71
4th yuga of 4

A maha-kalpa is followed by a maha-pralaya of equal length. Each kalpa is followed by a pralaya of equal length. Preceding the first and following each manvantara is a manvantara-sandhya, each with a length of Krita-yuga.
Hindu texts specify that the start and end of each of the yugas are marked by astronomical alignments. This cycle's Treta-yuga began with 5 planets residing in the "Aries" constellation. This cycle's Dvapara-yuga ended with the "Saptarshi" constellation residing in the "Magha" constellation. The current Kali-yuga will end with the Sun, Moon and Jupiter residing in the "Pushya" sector.

Human

The history of humanity is divided up into four yugas —, Treta Yuga|, Dvapara Yuga| and Kali-yuga—each with a 25% decline in dharmic practices and length, giving proportions of 4:3:2:1, indicating a de-evolution in spiritual consciousness and an evolution in material consciousness. Kali-yuga is followed by Satya-yuga of the next cycle, where a cycle is called a Yuga Cycle|. Each yuga is divided into a main period and two yuga-sandhis ⁠— and ⁠—where each yuga-sandhi lasts for 10% of the main period. Lengths are given in divine years, where a divine year lasts for 360 solar years. A chatur-yuga lasts for 4.32 million solar years with 1,728,000 years of Krita-yuga, 1,296,000 years of Treta-yuga, 864,000 years of Dvapara-yuga, and 432,000 years of Kali-yuga.

Current ''yuga''

Kali-yuga lasts for 432,000 years and is the 4th of 4 yugas in a cycle as well as the current yuga, with two sandhyas, each lasting for 36,000 years:

Kali-yuga started in 3102BCE:
Kali-yuga-sandhya ends in CE:
Kali-yuga-sandhyamsa starts in CE:
Kali-yuga ends in CE:
Current ''chatur yuga''

A chatur-yuga lasts for 4.32million years, where the current is the 28th of 71:

Started in BCE:
Ends in CE: