The metric system is based on the number ten.  Prefixes determine the power of ten.  Some prefixes are for numbers greater than one and others are used for numbers less than 1.    

 

Prefix

Abbreviation symbol

Power of ten

(Scientific notation)

Power of ten

(real number)

Yotta

Y

1024

1,000,000,000,000,000,000,000,000

Zetta

Z

1021

1,000,000,000,000,000,000,000

Exa

E

1018

1,000,000,000,000,000,000

Peta

P

1015

1,000,000,000,000,000

Tera

T

1012

1,000,000,000,000

Giga

G

109

10,000,000,000

Mega

M

106

1,000,000

myria

my

104

10,000

kilo

k

103

1000

hecto

h

102

100

daka

da

101

10

-

Base unit 1

100 = 1

1

deci

d

10-1

0.1

centi

c

10-2

0.01

milli

m

10-3

0.001

micro

u

10-6

0.000001

nano

n

10-9

0.000000001

pico

p

10-12

0.0000000000001

femto

f

10-15

0.0000000000000001

atto

a

10-18

0.0000000000000000001

zepto

z

10-21

0.0000000000000000000001

yocto

y

10-24

0.0000000000000000000000001

 

The seven basic units and their symbols and definitions are listed in the table below.

 

Variable

Metric / SI   symbol (name)

definition

length

m (meter)

The metre is the basic unit of length. It is the distance light travels, in a vacuum, in 1/299792458th of a second.

 

time

s(second)

The second is the basic unit of time. It is the length of time taken for 9192631770 periods of vibration of the caesium-133 atom to occur.

 

temperature

K (Kelvin)

The kelvin is the basic unit of temperature. It is 1/273.16th of the thermodynamic temperature of the triple point of water. It is named after the Scottish mathematician and physicist William Thomson 1st Lord Kelvin (1824-1907).

 

mass

kg (kilogram)

The kilogram is the basic unit of mass. It is the mass of an international prototype in the form of a platinum-iridium cylinder kept at Sevres in France. It is now the only basic unit still defined in terms of a material object, and also the only one with a prefix[kilo] already in place.

 

Electric current

A (ampere)

The ampere is the basic unit of electric current. It is that current which produces a specified force between two parallel wires which are 1 metre apart in a vacuum.It is named after the French physicist Andre Ampere (1775-1836).

 

Light intensity

Cd (Candela)

The candela is the basic unit of luminous intensity. It is the intensity of a source of light of a specified frequency, which gives a specified amount of power in a given direction.

Amount of substance

mol (mole)

The mole is the basic unit of substance. It is the amount of substance that contains as many elementary units as there are atoms in 0.012 kg of carbon-12.

 

 

There are many derived variables.  These variables come from combinations of the seven basic units.  The table below shows some of them.

 

variable

Unit (name/abbreviation)

area

Square meters (m2)

volume

Cubic meters (m3)

density

Kg / m3

speed

m /s

acceleration

m /s2

Specific volume

m3 / kg

concentration

Mol / m3

frequency

Hertz (Hz) = s-1

force

Newton (N) = kg m/s2

pressure

Pascal (Pa) = 1N /m2

power

Watt (W) = J/s = kg m2 / s3

Energy (heat)

Joule (J) = kg m2 / s2

Electric charge

Coulomb (c) = s A

Electric potential

Volt (V) = W / A

Electric resistance

Ohm  ( ) = V / A