Exa is a decimal unit prefix in the metric system denoting 10¹⁸ or 1000000000000000000. It was added as an SI prefix to the International System of Units (SI) in 1975,^[1] and has the unit symbol E.

Exa comes from the ancient Greek ἕξ héx, used as a prefix ἑξά- hexá-, meaning six (like hexa-), because it is equal to 1000⁶.

Examples:

The total storage needed by Gmail as of April 2012, ignoring backups and compression, is more than an exabyte (10,240 megabytes of storage per user multiplied by an estimated 260 million users)
1 EeV = 10¹⁸ electronvolts = 0.1602 joule
United States electric energy consumption is about 15 exajoule per year
1 exasecond is approximately 32 billion years
0.43 Es ≈ the approximate age of the universe
1 exametre is approximately 110 light-years
1.6 Em is 172 ± 12.5 light years—diameter of Omega Centauri (one of the largest-known globular clusters, perhaps containing over a million stars)^[2]^[3]
150 exahashes/s is the calculation rate of the Bitcoin network ≈ 150000000000000000000 hashes per second as of January 2021^[4]
1.5 exaFLOPS is the compute performance of the 'Frontier' supercomputer built by AMD and Cray for Oak Ridge National Laboratory^[5]

SI prefixes
v
t
e
Prefix		Base 10	Decimal	English word		Adoption ^{[nb 1]}
Name	Symbol	Base 10	Decimal	Short scale	Long scale	Adoption ^{[nb 1]}
quetta	Q	10³⁰	1000000000000000000000000000000	nonillion	quintillion	2022
ronna	R	10²⁷	1000000000000000000000000000	octillion	quadrilliard	2022
yotta	Y	10²⁴	1000000000000000000000000	septillion	quadrillion	1991
zetta	Z	10²¹	1000000000000000000000	sextillion	trilliard	1991
exa	E	10¹⁸	1000000000000000000	quintillion	trillion	1975
peta	P	10¹⁵	1000000000000000	quadrillion	billiard	1975
tera	T	10¹²	1000000000000	trillion	billion	1960
giga	G	10⁹	1000000000	billion	milliard	1960
mega	M	10⁶	1000000	million		1873
kilo	k	10³	1000	thousand		1795
hecto	h	10²	100	hundred		1795
deca	da	10¹	10	ten		1795
		10⁰	1	one		–
deci	d	10⁻¹	0.1	tenth		1795
centi	c	10⁻²	0.01	hundredth		1795
milli	m	10⁻³	0.001	thousandth		1795
micro	μ	10⁻⁶	0.000001	millionth		1873
nano	n	10⁻⁹	0.000000001	billionth	milliardth	1960
pico	p	10⁻¹²	0.000000000001	trillionth	billionth	1960
femto	f	10⁻¹⁵	0.000000000000001	quadrillionth	billiardth	1964
atto	a	10⁻¹⁸	0.000000000000000001	quintillionth	trillionth	1964
zepto	z	10⁻²¹	0.000000000000000000001	sextillionth	trilliardth	1991
yocto	y	10⁻²⁴	0.000000000000000000000001	septillionth	quadrillionth	1991
ronto	r	10⁻²⁷	0.000000000000000000000000001	octillionth	quadrilliardth	2022
quecto	q	10⁻³⁰	0.000000000000000000000000000001	nonillionth	quintillionth	2022
^ Prefixes adopted before 1960 already existed before SI. The introduction of the CGS system was in 1873.

See also

References