Metric Units
Symbols for units begin with a capital letter when they are named after an individual (for example, ampere, A; kelvin, K; hertz, Hz; coulomb, C). Otherwise they always begin with a lower case letter (for example, metre, m; second, s; mole, mol).
SI Metric Base Quantities and Units
There are seven base quantities in the SI system, with the following units:
Quantity 
Unit 
Symbol 
Length 
Meter 
m 
Mass 
Kilogram 
kg 
Time 
Second 
s 
Electric
Current 
Ampere 
A 
Temperature 
Kelvin 
K 
Luminous
intensity 
Candela 
cd 
Amount
of Substance 
Mole 
mol 
Derived Units with Special Names in the SI
Derived units
are formed by combining the base units according to the algebraic relations
linking the corresponding quantities. There is no set number of derived units,
as the possibilities are endless. The below 22 derived units have special names for convenience of reference, as they are frequently used.
Derived
Quantity 
Name of
Derived Unit

Symbol
for Unit

Expression in Terms
of Other Units 
plane angle

radian

rad 
m/m = 1

solid angle 
steradian

sr

m^{2}/m^{2} = 1

frequency

hertz

Hz

s^{1}

force

newton

N

m kg s^{2}

pressure, stress 
pascal

Pa 
N/m^{2} = m^{1} kg s^{2}

energy, work, amount of heat

joule

J 
N m = m^{2} kg s^{2}

power, radiant flux 
watt

W

J/s = m^{2} kg s^{3}

electric charge, amount
of electricity 
coulomb

C

sA

electric potential difference

volt

V

W/A = m^{2} kg s^{3}A^{1}

capacitance

farad

F 
C/V = m^{2} kg^{1} s^{4} A^{2}

electric resistance 
ohm

O 
V/A = m^{2} kg s3 A^{2}

electric conductance 
siemens 
S

A/V = m^{2} kg^{1} s^{3} A^{2}

magnetic flux 
weber

Wb

V s = m^{2} kg s^{2} A^{1}

magnetic flux density

tesla

T

Wb/m^{2} = kg s^{2} A^{1}

inductance

henry

H

Wb/A = m^{2} kg s^{2} A^{2}

Celsius temperature

degree Celsius

^{0}C

K

luminous flux

lumen

lm 
cd sr = cd

illuminance 
lux

lx

lm/m2 = m2 cd

activity referred to a radionuclide 
becquerel

Bq 
s^{1}

absorbed dose, specific energy
(imparted), kerma

gray

Gy

J/kg = m^{2} s^{2}

dose equivalent, ambient dose
equivalent 
sievert

Sv

J/kg = m^{2} s^{2}

catalytic activity 
katal 
kat

s^{1} mol

NonSI Units Accepted for Use with the International System of Units
There are many nonSI units that are accepted for use with the International
System, because they are widely used in everyday life, are of historical
importance or provide an advantage or convenience in a particular scientific,
technological or commercial specialty. Below are some nonSI units that are accepted for use with the International System because they are widely used with the SI in matters of everyday life. Their use is expected to continue indefinitely, and each has an exact definition in terms of an SI unit.
Quantity

Name of Unit

Symbol for Unit

Value in SI Units

Time 
Minute

min

1 min = 60 s


Hour

h

1 h = 60 min = 3600 s


Day

d

1 d = 24 h = 86 400 s

Plane angle

Degree

^{o} 
1^{o} = (p/180) rad


Minute

' 
1' = (1/60)^{o} = (p/ 10 800) rad


Second

"

1? = (1/60)' = (p/ 648 000) rad

Area 
Hectare

ha

1 ha = 1 hm^{2} = 10^{4} m^{2}

Volume

Liter

L, l

1 L = 1 l = 1 dm^{3} = 10^{3} cm^{3} = 10^{3} m^{3}

Mass 
Tonne

t

1 t = 10^{3} kg

Notes:
 Numerous other NonSI Units are accepted for use only in special circumstances. See the BIPM Brochure, International System of Units (SI).
 The symbol for the liter is an exception to the rule of using capital letters for symbols of units named after an individual. Either a lower case letter or a capital L may be used, the capital being allowed in this case to avoid confusion between the lower case letter l (el) and the number one, 1 (one).
 In English speaking countries, the tonne is usually called “metric ton”.
