This document defines 24 metric prefixes that are used to denote multiplication or division by powers of 10. It provides the name, symbol, and power of 10 for each prefix from yotta (1024) down to yocto (10-24). Examples are given for common uses of each prefix, such as a snow crystal being about 1 millimeter in diameter and the radius of atoms ranging from around 25 picometers for hydrogen.

1. METRIC PREFIX

2. Yotta
• Yotta is the largest unit prefix in the International System of Units (SI), denoting a factor of
1024.
• It has the unit symbol Y. The prefix name is derived from the Greek οκτώ (októ), meaning
eight, because it is equal to 10008.
• The total power output of the Sun is approximately 385 YW.

3. Zetta
• Zetta is a unit prefix in the metric system denoting a factor of 1021 .
• The prefix was added 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.
• The mass of Earth's atmosphere is approximately 5 zettagrams (Zg).

4. Exa
• Exa is a unit prefix in the metric system denoting 1018 .
• It was added to the International System of Units (SI) in 1975, and has the unit symbol E.
• Exa comes from the Greek ἕξ, used as a prefix ἑξά-, meaning six, because it is equal to 10006.
• 0.43 Es ≈ the approximate age of the Universe.

5. Peta
• Peta is a unit prefix in the metric system denoting multiplication by 1015 .
• It was adopted 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).
• The distance light travels in a year is 10 Pm.

6. Tera
• Tera is a unit prefix in the metric system denoting multiplication by 1012 .
• It has the symbol T. The prefix tera was confirmed for use in the SI in 1960.
• Tera is derived from Greek word τέρας teras, meaning “monster”.
• The orbit of Ceres is 1Tm.

7. Giga
• Giga is a unit prefix in the metric system denoting a factor of a billion, 109 .
• It has the symbol G.
• Giga is derived from the Greek word γίγας, meaning "giant".
• The orbit of the moon is measured in 1Gm.

8. Mega
• Mega is a unit prefix M in the metric system denoting a factor of one million, 106 .
• It was confirmed for use in the International System of Units (SI) in 1960.
• Mega comes from the Greek μέγας megas, meaning "great".
• The state of Florida is 1Mm.

9. Kilo
• Kilo is a unit prefix in the metric system denoting multiplication by one thousand.
• It has been 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, meaning "thousand".
• The Grand Coulee Dam is 1km.

10. Hecto
• Hecto or hecta is a unit prefix in the metric system denoting a factor of one hundred.
• Comes from the Greek ἑκατόν hekaton, meaning hundred.
• Its unit symbol in the International System of Units (SI) is the lower case letter h.
• The Court House is 1hm.

11. Deca
• Deca- or deka- (symbol da) is a prefix in the metric system, also a numerical prefix, denoting
a factor of ten.
• The term is derived from the Greek δέκα meaning "ten". Its symbol is the only SI prefix that
uses more than one character.
• The Oak tree is 1dam.

12. Deci
• Deci (symbol d) is a prefix in the metric system denoting a factor of one tenth.
• The prefix comes from the Latin decimus, meaning tenth.
• Its most frequent use is in the non-SI unit.
• The maple leaf can be measured in 1dm.

13. Centi
• Centi (symbol c) is a prefix in the metric system denoting a factor of one hundredth.
• The prefix comes from the Latin centum, meaning hundred.
• It is mainly used with the meter to express lengths in centimeters.
• A honeybee is about 1.3 centimeters in length.

14. Milli
• Milli (symbol m) is a prefix in the metric system denoting a factor of one thousandth (10-3).
• The prefix comes from the Latin mille, meaning one thousand.
• A snow crystal is about 1 millimeter in diameter.

15. Micro
• Micro (symbol μ) is a prefix in the metric system denoting a factor of 10−6 .
• The prefix comes from the Greek μικρός, meaning "small".
• It is the only SI prefix which uses a character not from the Latin alphabet.
• The size of the influenza virus is about 0.8 to 1.2.

16. Nano
• Nano- (symbol n) is an SI prefix meaning one billionth.
• Used primarily with the metric system, this prefix denotes a factor of 10−9.
• 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.

17. Pico
• Pico- (symbol p) is a prefix in the metric system denoting one trillionth, a factor of 10−12 .
• Derived from the Spanish pico, meaning peak, beak, bit.
• The radius of atoms range from ~25 picometers (hydrogen).

18. Femto
• Femto- (symbol f) is a prefix in the metric system denoting a factor of 10−15 .
• It was added in 1964 to the SI.
• It is derived from the Danish word femten, meaning "fifteen".
• A proton as a diameter of about 1.6 to 1.7 femtometres.

19. Atto
• Atto- (symbol a) is a prefix in the metric system denoting a factor of 10−18 .
• It is derived from the Danish word atten, meaning "eighteen".
• Weight of the HIV-1 Virus is about 1 ag.

20. Zepto
• Zepto- (symbol z) is a prefix in the metric system denoting a factor of 10−21 .
• It comes from the Latin septem, meaning "seven", since it is equal to 1000−7.
• The human insulin molecule is roughly 10 zeptograms.

21. Yocto
• Yocto (symbol y) is a prefix in the metric system denoting a factor of 10−24 .
• It comes from the Latin/Greek octo (οκτώ), meaning "eight", because it is equal to 1000−8.
• Rest mass of proton:1.6726 yg