SI Units – Système International d’Unités
the modern scientific system of units
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SI Units
| Unit |
Symbol |
Quantity |
| ampere |
A |
electric current |
| becquerel |
Bq |
radioactivity |
| candela |
cd |
luminous intensity |
| coulomb |
C |
electric charge, electric flux |
| farad |
F |
electrical capacitance |
| gray |
Gy |
absorbed dose of ionizing radiation |
| henry |
H |
inductance |
| hertz |
Hz |
frequency |
| joule |
J |
work, energy and heat |
| katal |
kat |
catalytic activity |
| kelvin |
K |
thermodynamic temperature |
| kilogram |
kg |
mass |
| lumen |
lm |
luminous flux |
| lux |
lx |
illuminance |
| metre |
m |
length |
| mole |
mol |
amount of substance |
| newton |
N |
force |
| ohm |
Ω |
electric resistance, impedance, reactance |
| pascal |
Pa |
pressure, stress |
| radian |
rad |
plane angle |
| second |
s |
time |
| siemens |
S |
electrical conductance |
| sievert |
Sv |
radiation dose equivalent |
| steradian |
sr |
solid angle |
| tesla |
T |
magnetic flux density, magnetic induction, magnetic field strength |
| volt |
V |
electromotive force, electric potential, potential difference |
| watt |
W |
power, radiant flux |
| weber |
Wb |
magnetic flux |
Base SI units are shown in red, all other units are derived
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Other Units
| Unit |
Symbol |
Quantity / Notes |
| ångström |
Å |
wavelength of light, ultraviolet rays, X-rays, molecular and atomic distances |
| are |
a |
land measure = 100 sq metres |
| astronomical unit |
au |
the earth’s mean distance from the sun, about 92.9 million miles |
| bar |
bar |
atmospheric pressure |
| barn |
b |
effective cross-sectional area of a nucleus for the capture of neutrons |
| bel |
B |
relationship between two power levels |
| curie |
Ci |
former unit of radioactivity |
| day |
d |
time = 24 hours |
| degree |
° |
angle = 1/360 of a circle = 60 minutes |
| degree Celsius |
ºC |
temperature = 1 kelvin |
| electronvolt |
eV |
energy acquired by an electron when accelerated by a potential of one volt |
| hectare |
ha |
land measure = 100 ares or 10000 sq metres |
| hour |
h |
time = 1/24 of a day = 60 minutes |
| knot |
|
1 nautical mile per hour |
| litre |
L |
volume = 1 cubic decimetre = 1000 cubic centimetres |
| metric ton |
|
see tonne |
| minute |
min |
time = 1/60 of an hour = 60 seconds |
| minute |
‘ |
angle = 1/60 of a degree = 60 seconds |
| nautical mile |
|
one minute of latitude measured along a meridian |
| neper |
Np |
ratio of two currents, two voltages, etc |
| oersted |
Oe |
magnetic field strength |
| rad |
rad |
former unit of absorbed radiation dose |
| rem |
rem |
former unit of radiation dosage |
| roentgen / röntgen |
R |
dose of X-rays or gamma rays |
| second |
” |
angle = 1/60 of a minute |
| tonne / metric ton |
t |
mass = 1000 kilograms |
| unified atomic mass unit |
u |
approximate mass of a hydrogen atom, a proton, or a neutron |
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SI Prefixes
| Prefix |
Symbol |
Exponent (base 10) |
| yotta |
Y |
24 |
| zetta |
Z |
21 |
| exa |
E |
18 |
| peta |
P |
15 |
| tera |
T |
12 |
| giga |
G |
9 |
| mega |
M |
6 |
| kilo |
k |
3 |
| hecto |
h |
2 |
| deca |
da |
1 |
|
|
0 |
| deci |
d |
-1 |
| centi |
c |
-2 |
| milli |
m |
-3 |
| micro |
µ |
-6 |
| nano |
n |
-9 |
| pico |
p |
-12 |
| femto |
f |
-15 |
| atto |
a |
-18 |
| zepto |
z |
-21 |
| yocto |
y |
-24 |
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Created 11 April 2010