Zepto (unit symbol z) is a unit prefix in the metric system denoting a factor of 10−21 or 0.000000000000000000001.

Adopted in 1991, it comes from the Latin septem, meaning "seven", since it is equal to 1000−7.

Examples of its use:

Prefix Base 1000 Base 10 Decimal English word Adoption[nb 1]
Name Symbol Short scale Long scale
yotta Y  10008  1024 1000000000000000000000000  septillion  quadrillion 1991
zetta Z  10007  1021 1000000000000000000000  sextillion  trilliard 1991
exa E  10006  1018 1000000000000000000  quintillion  trillion 1975
peta P  10005  1015 1000000000000000  quadrillion  billiard 1975
tera T  10004  1012 1000000000000  trillion  billion 1960
giga G  10003  109 1000000000  billion  milliard 1960
mega M  10002  106 1000000  million 1873
kilo k  10001  103 1000  thousand 1795
hecto h  10002/3  102 100  hundred 1795
deca da  10001/3  101 10  ten 1795
 10000  100 1  one
deci d  1000−1/3  10−1 0.1  tenth 1795
centi c  1000−2/3   10−2 0.01  hundredth 1795
milli m  1000−1  10−3 0.001  thousandth 1795
micro μ  1000−2  10−6 0.000001  millionth 1873
nano n  1000−3  10−9 0.000000001  billionth  milliardth 1960
pico p  1000−4  10−12 0.000000000001  trillionth  billionth 1960
femto f  1000−5  10−15 0.000000000000001  quadrillionth  billiardth (Proposed) 1964
atto a  1000−6  10−18 0.000000000000000001  quintillionth  trillionth 1964
zepto z  1000−7  10−21 0.000000000000000000001  sextillionth  trilliardth 1991
yocto y  1000−8  10−24  0.000000000000000000000001  septillionth  quadrillionth 1991
  1. ^ Prefixes adopted before 1960 already existed before SI. 1873 was the introduction of the CGS system.


  1. ^ Professor John Dell, Slide 2: https://www.engineersaustralia.org.au/sites/default/files/shado/Learned%20Groups/Colleges/Mechanical%20College/WA%20Branch/Mechanical%20Engineering%20Gone%20Small%20(Presentation%20with%20Audio).pdf

Agglutination-PCR (ADAP) is an ultrasensitive solution-phase method for detecting antibodies. Antibodies bind to and agglutinate synthetic antigen–DNA conjugates, enabling ligation of the DNA strands and subsequent quantification by qPCR. Like other Immuno-PCR (IPCR) detection methods ADAP combines the specificity of antibody-antigen recognition and the sensitivity of PCR. ADAP detects zepto- to attomoles of antibodies in 2 μL of sample with a dynamic range spanning 5–6 orders of magnitude. For example, ADAP allows to detect anti-thyroglobulin autoantibodies from human patient plasma with a 1000-fold increased sensitivity over an FDA-approved radioimmunoassay. ADAP also allows to simultaneously detect multiple antibodies in one experiment, much more than ELISA or radioimmunoassay.

The study published in the ACS Central Science journal mentioned that this testing method is 10,000 times more effective than the existing diagnostic techniques.Another advantage of ADAP method is the simplicity. It can be adapted to such a cheap equipment as, for example, SlipChip. It does not require complex and expensive equipment, it does not require working with hazardous radioactive reagents.


Atto (symbol a) is a unit prefix in the metric system denoting a factor of 10−18 or 0.000000000000000001.

The unit multiple was adopted at the 12th General Conference on Weights and Measures (CGPM) in Resolution 8. It is derived from the Danish word atten, meaning "eighteen".

Examples of its use:

Weight of the HIV-1 virus is about 1×10−18 kg or 1×10−15 g, which can be written as 1 fg or 1000 ag.

More examples available.


Femto- (symbol f) is a unit prefix in the metric system denoting a factor of 10−15 or 0.000000000000001. Adopted by the 11th General Conference on Weights and Measures, it was added in 1964 to the SI. It is derived from the Danish word femten, meaning "fifteen".

Examples of use:

The HIV-1 virus has the mass of about 1 x 10−15 g or 1 fg. Orders of magnitude (mass)

a proton has a diameter of about 1.6 to 1.7 femtometres.

More examples available.The femtometre shares the unit symbol (fm) with the older non-SI unit fermi, to which it is equivalent. The fermi, named in honour of Enrico Fermi, is often encountered in nuclear physics.

Foundation (framework)

Foundation is a responsive front-end framework. Foundation provides a responsive grid and HTML and CSS UI components, templates, and code snippets, including typography, forms, buttons, navigation and other interface elements, as well as optional functionality provided by JavaScript extensions. Foundation is maintained by ZURB and is an open source project.

JQT (software)

jQT (formerly jQTouch) is an open-source Zepto/ JQuery plugin with native animations, automatic navigation, and themes for mobile WebKit browsers like iPhone, G1 (Android), and Palm Pre. It enables programmers to develop mobile applications with a native look and feel for the target device using HTML, CSS, and JavaScript.

jQT tries to emulate mobile platforms, like the iOS SDK, as much as possible even enabling the use of the Webkit application offline.


Kilo is a decimal unit prefix in the metric system denoting multiplication by one thousand (103). It is used in the International System of Units where it has the unit symbol k, in lower case.

The prefix kilo is derived from the Greek word χίλιοι (chilioi), meaning "thousand". It was originally adopted by Antoine Lavoisier's research group in 1795, and introduced into the metric system in France with its establishment in 1799.

In 19th century English it was sometimes spelled chilio, in line with a puristic opinion by Thomas Young


Locky is ransomware malware released in 2016. It is delivered by email (that is allegedly an invoice requiring payment) with an attached Microsoft Word document that contains malicious macros. When the user opens the document, it appears to be full of garbage, and includes the phrase "Enable macro if data encoding is incorrect," a social engineering technique. If the user does enable macros, they save and run a binary file that downloads the actual encryption trojan, which will encrypt all files that match particular extensions. Filenames are converted to a unique 16 letter and number combination. Initially, only the .locky file extension was used for these encrypted files. Subsequently, other file extensions have been used, including .zepto, .odin, .aesir, .thor, and .zzzzz. After encryption, a message (displayed on the user's desktop) instructs them to download the Tor browser and visit a specific criminal-operated Web site for further information. The Web site contain instructions that demand a payment of between 0.5 and 1 bitcoin (as of November 2017, one bitcoin varies in value between $9,000 and $10,000 via a bitcoin exchange). Since the criminals possess the private key and the remote servers are controlled by them, the victims are motivated to pay to decrypt their files.


Mega is a unit prefix in metric systems of units denoting a factor of one million (106 or 1000000). It has the unit symbol M. It was confirmed for use in the International System of Units (SI) in 1960. Mega comes from Ancient Greek: μέγας, translit. megas, lit. 'great'.

Names of small numbers

This article lists and discusses the usage and derivation of names of small numbers.


Nano- (symbol n) is a unit prefix meaning "one billionth". Used primarily with the metric system, this prefix denotes a factor of 10−9 or 0.000000001. It is frequently encountered in science and electronics for prefixing units of time and length.


One nanometer is about the length that a fingernail grows in one second.

Three gold atoms lined up are about one nanometer long.

If a toy marble were scaled down to one nanometer wide, Earth would scale to about one meter (3.3 feet) wide.

One nanosecond is about the time required for light to travel 30 cm in air, or 20 cm in an optical fiber.The prefix derives from the Greek νᾶνος (Latin nanus), meaning "dwarf". The General Conference on Weights and Measures (CGPM) officially endorsed the usage of nano as a standard prefix in 1960.

When used as a prefix for something other than a unit of measure (as for example in words like "nanoscience"), nano refers to nanotechnology, or means "on a scale of nanometres". See nanoscopic scale.

Newton (unit)

The newton (symbol: N) is the International System of Units (SI) derived unit of force. It is named after Isaac Newton in recognition of his work on classical mechanics, specifically Newton's second law of motion.

See below for the conversion factors.

Orders of magnitude (charge)

This page is a progressive and labeled list of the SI charge orders of magnitude, with certain examples appended to some list objects.


Peta () is a decimal unit prefix in the metric system denoting multiplication by 1015 (1000000000000000). It was adopted as an SI prefix in the International System of Units in 1975, and has the symbol P.

Peta is derived from the Greek πέντε, meaning "five". It denotes the fifth power of 1000 (10005). It is similar to the prefix penta ("five"), but without the letter n (on the analogy of the prefix tera [from the Greek for "monster"] for 10004 looking like tetra- ["four"] with a letter missing).


1 petametre = 1015 metres

1 petasecond = 1015 seconds (31.7 million years)

1 petahertz = 1015 cycle per second. Visible light is around 0.5 PHz.

1 petabyte = 1015 bytes

the mass–energy equivalence is 89.9 PJ/kg

1 light-year = 9.461 Pm


Pico- (symbol p) is a unit prefix in the metric system denoting one trillionth, a factor of 10−12 (0.000000000001).

Derived from the Spanish pico, meaning peak, beak, bit, this was one of the original 12 prefixes defined in 1960 when the International System of Units was established.The radius of atoms range from 25 picometers (hydrogen) to 260 picometers (caesium). One picolight-year is about nine kilometers (six miles).


Tera is a unit prefix in the metric system denoting multiplication by 1012 or 1000000000000 (one trillion short scale; one billion long scale). It has the symbol T. Tera is derived from Greek word τέρας teras, meaning "monster". The unit prefix was confirmed for use in the International System of Units (SI) in 1960.

Examples of its use:

terahertz radiation: electromagnetic waves within the band of frequencies from 0.3 to 3 THz. Visible light is around 500 THz.

terabit and terabyte, units used in data storage.

teragram: equal to 109 kg. The Great Pyramid of Giza has a mass of about 6 Tg.

terasecond: approximately 31,558 years

teralitre: equal to 109 m3. Lake Zurich contains about 4 TL of water.

terawatt: used to measure total human energy consumption. In 2010 it was 16 TW (TJ/s).

terametre (= 1,000,000,000 km): Light travels 1.079 Tm in one hour.

Unit prefix

A unit prefix is a specifier or mnemonic that is prepended to units of measurement to indicate multiples or fractions of the units. Units of various sizes are commonly formed by the use of such prefixes. The prefixes of the metric system, such as kilo and milli, represent multiplication by powers of ten. In information technology it is common to use binary prefixes, which are based on powers of two. Historically, many prefixes have been used or proposed by various sources, but only a narrow set has been recognised by standards organisations.


Yotta is the largest decimal unit prefix in the metric system, denoting a factor of 1024 or 1000000000000000000000000; that is, one million million million million, or one septillion. It has the unit symbol Y. The prefix name is derived from the Ancient Greek οκτώ (októ), meaning "eight", because it is equal to 1,0008. It was added as an SI prefix to the International System of Units (SI) in 1991.Usage examples:

The mass of the Earth is 5,972.6 Yg.

The mass of the oceans is about 1.4 Yg.

The total power output of the Sun is approximately 385 YW.

The observable universe is estimated to be 880 Ym in diameter.

One yottabyte (YB) is a unit of digital information or information storage capacity that contains one septillion bytes or 1,000 zettabytes. The yobibyte (YiB) is a related unit that uses a binary prefix, and means 1,0248 bytes, which is approximately 1.2 septillion bytes.


Zetta is a decimal unit prefix in the metric system denoting a factor of 1021 or 1000000000000000000000. The prefix was added as an SI prefix to the International System of Units (SI) in 1991 and has the symbol Z.

Zetta is evocative of the Latin numeral septem, meaning "seven". Therefore it was used to denote the seventh power of 1000.A prefix of the same value, hepta, was informally introduced a few years before the promulgation of zetta. It was formed from the Greek ἑπτά (hepta), also meaning "seven". Hepta never received official sanction and is obsolete. Zeta (ζήτα), although the 6th letter of the modern and classical Greek alphabet, denotes a value of seven (7) when used as a numeral.


The mass of Earth's atmosphere is approximately 5 zettagrams (Zg).

The volume of seawater in the Earth's oceans is approximately 1.369 zettalitres (ZL).

The Avogadro constant is 602.2 Zmol−1.

Estimates of the diameter of the Milky Way Galaxy are between 0.9 and 1.7 zettametres (Zm).

A zettabyte (ZB) is a quantity of information or information storage capacity equal to 1021 bytes, 10007 bytes, 1,000 exabytes or 1 sextillion bytes. The zebibyte (ZiB) is a related unit that uses a binary prefix, and means 10247 bytes.

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