(See also Metric/Imperial Conversion Charts and Unit Converter)

## What is kilo, mega, giga, tera … ?

In the Metric System there are standard ways to talk about big and small numbers:

- “kilo” for a thousand,
- “mega” for a million,
- and more …

### Example: A long rope measures **one thousand** meters

It is easier to say it is 1 **kilo**meter long,

and even easier to write it down as **1 km**.

So we used ** kilo** in front of the word

**to make**

*meter**“*.

**kilometer**“And the abbreviation is “* km*” (

*for kilo and*

**k***for meter, put together).*

**m**### Some more examples:

Example: You put your bag on a set of scales and it shows 2000 grams, we can call that 2 **kilograms**, or simply 2 kg.

### Example: Teaspoon

A teaspoon holds 5 **thousandths** of a liter (5**1000** of a liter), but it is better to say “5 **milli**liters”, or write it simply as **5 mL**.

“kilo”, “mega”, “milli” etc are called “prefixes”:

**Prefix**: a word part that can be added to the beginning of another word to create a new word

So, using the prefix “milli” in front of “liter” creates a new word “milliliter”.

Here we list the prefix for commonly used big and small numbers:

### Common Big and Small Numbers

Name |
The Number |
Prefix |
Symbol |

trillion | 1,000,000,000,000 | tera | T |

billion | 1,000,000,000 | giga | G |

million | 1,000,000 | mega | M |

thousand | 1,000 | kilo | k |

hundred | 100 | hecto | h |

ten | 10 | deka | da |

unit |
1 |
||

tenth | 0.1 | deci | d |

hundredth | 0.01 | centi | c |

thousandth | 0.001 | milli | m |

millionth | 0.000 001 | micro | µ |

billionth | 0.000 000 001 | nano | n |

trillionth | 0.000 000 000 001 | pico | p |

- Just remember for large values (each one a thousand times bigger):
- “kilo mega giga tera”
- and for small values (each one a thousand times smaller):
- “milli micro nano pico”

### Try To Do Some Yourself!

- How do you refer to a million liters?
- How about one
**billionth**of a meter?

See the bottom of this page for more questions to challenge yourself …

### How Big Are They?

- There is a lot of difference between them.
Think in terms of time:

- A million seconds is about
**12 days**A billion seconds is about**32 years** - A longer list:

- A
**thousand**seconds is about a**quarter of an hour** - A
**million**seconds is about**12 days** - A
**billion**seconds is about 32 years, almost**half a lifetime** - A
**trillion**seconds is about 32,000 years (the last Ice Age finished 12,000 years ago)

### Much Bigger and Smaller

There are also prefixes for much bigger and smaller numbers:

### Some Very Big, and Very Small Numbers

Name |
The Number |
Prefix |
Symbol |

Very Big ! | |||

septillion | 1,000,000,000,000,000,000,000,000 | yotta | Y |

sextillion | 1,000,000,000,000,000,000,000 | zetta | Z |

quintillion | 1,000,000,000,000,000,000 | exa | E |

quadrillion | 1,000,000,000,000,000 | peta | P |

Very Small ! | |||

quadrillionth | 0.000 000 000 000 001 | femto | f |

quintillionth | 0.000 000 000 000 000 001 | atto | a |

sextillionth | 0.000 000 000 000 000 000 001 | zepto | z |

septillionth | 0.000 000 000 000 000 000 000 001 | yocto | y |

Also see Lengths From Very Small to Very Large |

### All Big Numbers We Know

Name |
As a Power of 10 |
As a Decimal |

Thousand | 103 | 1,000 |

Million | 106 | 1,000,000 |

Billion | 109 | 1,000,000,000 |

Trillion | 1012 | 1,000,000,000,000 |

Quadrillion | 1015 | etc … |

Quintillion | 1018 | |

Sextillion | 1021 | |

Septillion | 1024 | |

Octillion | 1027 | |

Nonillion | 1030 | |

Decillion | 1033 | |

Undecillion | 1036 | |

Duodecillion | 1039 | |

Tredecillion | 1042 | |

Quattuordecillion | 1045 | |

Quindecillion | 1048 | |

Sexdecillion | 1051 | |

Septemdecillion | 1054 | |

Octodecillion | 1057 | |

Novemdecillion | 1060 | |

Vigintillion | 1063 | 1 followed by 63 zeros! |

- And a
**Googol**is 1 followed by one hundred zeros (10100) : -
*10,000,000,000,000,000,000,000,000,000,000,000, 000,000,000,000,000,000,000,000,000,000,000,* *000,000,000,000,000,000,000,000,000,000,000*

Then there is the **Googolplex**. It is 1 followed by* Googol zeros*. I can't even write down the number, because there is not enough matter in the universe to form all the zeros:

10,000,000,000,000,000,000,000,000,000,000, … (Googol number of Zeros)

And a **Googolplexian** is a 1 followed by* Googolplex zeros*. Wow.

### All Small Numbers We Know

Name |
As a Power of 10 |
As a Decimal |

thousandths | 10-3 | 0.001 |

millionths | 10-6 | 0.000 001 |

billionths | 10-9 | 0.000 000 001 |

trillionths | 10-12 | etc … |

quadrillionths | 10-15 | |

quintillionths | 10-18 | |

sextillionths | 10-21 | |

septillionths | 10-24 | |

octillionths | 10-27 | |

nonillionths | 10-30 | |

decillionths | 10-33 | |

undecillionths | 10-36 | |

duodecillionths | 10-39 | |

tredecillionths | 10-42 | |

quattuordecillionths | 10-45 | |

quindecillionths | 10-48 | |

sexdecillionths | 10-51 | |

septemdecillionths | 10-54 | |

octodecillionths | 10-57 | |

novemdecillionths | 10-60 | |

vigintillionths | 10-63 |

Copyright © 2018 MathsIsFun.com

## Definitions of the SI units: The twenty SI prefixes

It is important to note that the kilogram is the only SI unit with a prefix as part of its name and symbol.

Because multiple prefixes may not be used, in the case of the kilogram the prefix names of Table 5 are used with the unit name “gram” and the prefix symbols are used with the unit symbol “g.

” With this exception, any SI prefix may be used with any SI unit, including the degree Celsius and its symbol °C.

Example 1: |
10-6 kg = 1 mg (one milligram), but not 10-6 kg = 1 µkg (one microkilogram) |

Example 2: |
Consider the earlier example of the height of the Washington Monument. We may write hW = 169 000 mm = 16 900 cm = 169 m = 0.169 km using the millimeter (SI prefix milli, symbol m), centimeter (SI prefix centi, symbol c), or kilometer (SI prefix kilo, symbol k). |

Because the SI prefixes strictly represent powers of 10, they should not be used to represent powers of 2. Thus, one kilobit, or 1 kbit, is 1000 bit and **not** 210 bit = 1024 bit. To alleviate this ambiguity, prefixes for binary multiples have been adopted by the International Electrotechnical Commission (IEC) for use in information technology.

** Continue to **Units outside the SI

## Numerical Prefixes

Cite

A prefix is a syllable at the beginning of a word. A numerical prefix lets you know how many there are of a particular thing. Here are some common numerical prefixes.

PrefixPrefix meaningSample wordsuni- | 1 | unicorn: mythical creature with one horn |

mono- | 1 | monorail: train that runs on one track |

bi- | 2 | bicycle: two-wheeled vehicle |

tri- | 3 | triceratops: three-horned dinosaur |

quadr- | 4 | quadruped: four-footed animal |

quint- | 5 | quintuplets: five babies born at a single birth |

penta- | 5 | pentagon: figure with five sides |

hex- | 6 | hexapod: having six legs, an insect, for example |

sex- | 6 | sextet: group of six musicians |

hept- | 7 | heptathlon: athletic contest with seven events |

sept- | 7 | septuplets: seven babies at a single birth |

octo- | 8 | octopus: sea creature with eight arms |

novem- | 9 | novena: prayers said over nine days |

deka- or deca- | 10 | decade: a period of 10 years |

cent- | hundred | century: a period of 100 years |

hecto- | hundred | hectogram: 100 grams |

milli- | thousand | millennium: a period of 1,000 years |

kilo- | thousand | kilogram: 1,000 grams |

mega- | million | megaton: one million tons |

giga- | billion | gigawatt: one billion watts |

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## Prefixes: Definition & Examples – Video & Lesson Transcript | Study.com

Even Mrs. Brown's careful *oversight* couldn't prevent some of her students from causing trouble at the science fair. In *hindsight,* Jesse's decision to use real live dynamite in her science project, showed a lack of *insight.* Hopefully, next time she'll have the *foresight* to try a less explosive experiment.

In these three sentences, can you see how there are four words that all include 'sight' but all four of them have different beginnings? Those different beginning parts are called prefixes. **Prefixes** are groups of letters added to the beginning of a word to change its meaning.

In these sentences, we have four prefixes attached to 'sight' – 'over,' 'hind,' 'in,' and 'fore.' 'Sight' is called the **root word**, the word that the prefixes are attached to.

'Sight' is a perfectly good word all on its own but you can add prefixes to it to create a whole new word that builds on the original root word.

Oversight = over + sight

Here the prefix 'over' gives you an idea of a high place. When you combine that with 'sight,' you get the idea of looking down at someone from a high place, or supervising them.

So 'oversight' means watching someone to make sure they're doing what they are supposed to. Mrs.

Brown was supposed to have 'oversight' for her class but she missed Jessie's volcano.

Hindsight = hind + sight

Think about the word 'behind.' 'Hind' means 'backwards,' so if you are looking backwards, you're looking into the past. For Jessie, after her volcano explodes, she's looking back into the past to say, 'hey maybe that was a bad plan after all.'

Insight = in + sight

If you think about the motion of going in, or looking in, it means that you're going closer to the center of something, so 'insight' means looking deeper into the center or seeing what's really there. That's exactly what Jessie didn't do when she decided to put dynamite in her volcano.

Foresight = fore + sight

Think about the word 'forward.' 'Fore' is motion into the future. Foresight is the opposite of hindsight; it's looking into the future to understand what's going to happen. Hopefully for Jessie's next project, she'll look into the future and think about what will happen before she tries it.

These four words are examples of how you can make completely different words by attaching different prefixes to a root word.

## Number and Quantity Prefixes

A prefix is a part of a word that is added to the beginning of another word to change its meaning. These syllables aren't usually words on their own, but they are very important when it comes to understanding new words in English.

Many prefixes have to do with numbers and quantities. Learning to recognize these number prefixes and memorizing their meanings will make it easier to figure out what unfamiliar words mean. If you already know the root word, you can often decode the definition by putting the meaning of the prefix and root word together.

When you are able to commit a numerical prefix to memory, it becomes much easier to decipher the meaning of unfamiliar words that use that prefix. If you know that “tri” represents the number three, then it's easy to figure out that “tricycle” is something that has three wheels.

Listed below are several of the most common number prefixes, along with the number they represent and some example words that contain that numerical prefix.

Prefix | Number | Examples |

milli- | .001 | millimeter, milliliter, millipede, millisecond, milliampere, milligram, milliwatt, millivolt |

centi- | .01 | centimeter, centigrade, centiliter, centigram, centipede, centile |

deci- | .1 | decibel, decimate (historically, to kill 1 in 10 of the enemy), deciliter, decimeter, decigram |

semi-hemi- | .5 | semester, semicircle, semiannual, semiautonomous, semiautomatic, semiconscious, semicolonhemisphere, hemiplegic, hemicycle |

uni-mono- | 1 | unicycle, unicorn, universe, universal, unilateral, union, unicellular, uniformmonotone, monocle, monogram, monosodium, monochromatism, monopoly, monoglyceride, monosyllabic, monotony |

bi-di- | 2 | bliateral, bicycle, bigamy, bisexual, bipedal, bipartisan, bipod, binary, bisect, bifocal, bilingualdipthong, dissect, dioxide, diptych, digital, divide, division |

tri- | 3 | tricycle, triathlon, tripod, triglyceride, triangle, trigonometry, triangulation, trilingual, triumvirate, trillion |

quad-, quart-tetra- | 4 | quadruped, quadruple, quadrillion, quadriplegic, quadrennially, quadrant, quadricep, quadratic, quadruplet, quadrilateralquartet, quarter, quarterfinal, quarterback, quartile,tetrameter, Tetris, tetrachloride, tetrahedrite, tetrahedron, tetrameter, tetragram, tetragonal, tetrapod |

quint-penta- | 5 | quintuplets, quintessential, quintile, quintessence, quintuplet, quintainpentagon, pentathlon, pentathlete, pentameter, pentagram, pentahedron, pentacle, pentanol |

sext-hex- | 6 | sextet, sextant, sextette, sextains, ssextilehexagon, hexidecimal, hexahedron, hexameters, hexachord, hexagram, hexapod |

sept-hept- | 7 | septuagenarian, September, septennial, septuplets, septarian, septetheptathlon, heptameter, heptagonal, heptane, heptose |

oct- | 8 | octogon, octopus, octogenarian, October, octosyllabic, octapeptide, octahedron, octameter, octuplet, octuplex |

non-, nov-ennea- | 9 | nonagon, novenas (9 days before Christmas in Mexico), nonagenarian, nonapeptide, nonoseenneagram, enneagon, enneadic |

dec- | 10 | decathlon, decade, December, decasyllabic, decahedron, decaliter, decapod |

cent- | 100 | century, centennial |

kilo | 1000 | kilometer, kilogram, kilocalories, kilojoules, kilowatt, kilovolt, kilobar, kilobye |

multi-poly- | many | multipurpose, multiply, multicurrency, multifunctional, multimolecular, multiregional, multifacetedpolygon, polygamy, polymer, polyester, polycarbonate, polypropylene, polyurethane, polymorphism, polynomial |

Note that some numbers have more than one prefix. This is because English draws from both Greek and Latin influences, and those languages have two different numbering systems – both of which are used for English prefixes. In the chart above, the Latin prefix is always listed above the Greek one when both are in use.

For example, “quint” as in “quintuplets” (a group of five babies born to the same mother at once) is derived from the Greek. By contrast, “penta” as in “pentagon” (a five-sided polygon) is derived from the Latin.

Memorizing number prefixes will help you quickly figure out what new words mean, particularly when it comes to math and science applications. The metric system also makes use of many Latin prefixes to express extremely large or extremely small quantities; you can read more about metric prefixes here.

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