Metric Numbers

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 kilometer long,

and even easier to write it down as 1 km.

So we used kilo in front of the word meter to make "kilometer".

And the abbreviation is "km" (k for kilo and m for meter, put together).

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 (51000 of a liter), but it is better to say "5 milliliters", 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 ยต
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
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

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
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 observable 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 ...
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

5627,5632,1927,1928,1929,1930,3473,3474,3475,3476