“What are the SI Base Units ?
What are the SI Derived Units ?
What are the SI units Prefixes ?
You all must have this kind of questions in your mind nowadays. Below article will solve this puzzle of yours. Just take a look.”
The SI or System International has the set of seven base units. These have been chosen to fulfill the requirements for science and technology measurements. The selection of seven base units is the responsibility of the International Committee of Weights and Measures (CIPM).
The International System of Units (SI) is the modern form of the metric system of units of measurement built on seven base units, which are the ampere, kelvin, second, metre, kilogram, candela, mole, and a set of twenty prefixes to the unit names and unit symbols that may be used when specifying multiples and fractions of the units. The system also specifies names for 22 derived units, such as lumen and watt, for other common physical quantities.
There are seven, dimensionally independent, base SIunits and two supplementary units. All other units can be derived from the base ones. Below, you can find the list of the base SI units as well as the list of the Supplementary SI units.
SI Base Units  
Unit  Symbol  Quantity 
Meter (metre)  m  Length 
Kilogram  kg  Mass 
Second  s  Time 
Ampere  A  Electric current 
Kelvin  K  Thermodynamic temperature 
Mole  mol  Amount of substance 
Candela  cd  Luminous intensity 
SI Supplementary Units  
Radian  rad  Plane angle (2D angle) 
Steradian  sr  Solid angle (3D angle) 
SI Unit Definitions :
(1) Metre: The metre is the length of the path traveled by light in vacuum during a time interval of 1/299,792,458 second.
(2) Kilogram: The kilogram is the unit of mass equal to the mass of the international prototype of kilogram.
(3) Second: The second is the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levers (F=4, m_{F}=0 to F=3, m_{F}=0) of the ground state of the cesium 133 atom.
(4) Ampere: The ampere is the constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular crosssection, and placed 1 metre apart in vacuum, would produce between these conductors a force equal to 2×10^{7} Newton per meter of length.
(5) Kelvin: The Kelvin, unit of thermodynamic temperature is the fraction 1/273.16 of the thermodynamic temperature of the triple point of water.
(6) Mole: The mole is the mount of substance of a system which contains as many elementary entities as there are atoms in .012 kg of carbon 12 (about 6.022×10^{23} atoms). When the mole is used, the elementary entities must be specified and may be atoms, molecules, ions, electrons, other particles, or specified groups of such particles.
(7) Candela: The candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540×10^{12} Hz and that has a radiant intensity in that direction of 1/683 watt per steradian.
SI derived units are units of measurement derived from the seven base units specified by the International System of Units (SI). They are either dimensionless or can be expressed as a product of one or more of the base units, possibly scaled by an appropriate power of exponentiation.
The SI has special names for 22 of these derived units (for example, hertz, the SI unit of measurement of frequency). The names of SI derived units, when written in full, are in lowercase. However, the symbols for units named after persons are written with an uppercase initial letter. For example, the symbol for hertz is “Hz”; but the symbol for metre is “m”.
Name  Symbol  Quantity  Equivalents  SI base unit Equivalents 
hertz  Hz  frequency  1/s  s^{−1} 
radian  rad  angle  m/m  1 
steradian  sr  solid angle  m^{2}/m^{2}  1 
newton  N  force, weight  kg⋅m/s^{2}  kg⋅m⋅s^{−2} 
pascal  Pa  pressure, stress  N/m^{2}  kg⋅m^{−1}⋅s^{−2} 
joule  J  energy, work, heat  N⋅m C⋅V W⋅s 
kg⋅m^{2}⋅s^{−2} 
watt  W  power, radiant flux  J/s V⋅A 
kg⋅m^{2}⋅s^{−3} 
coulomb  C  electric charge or quantity of electricity  s⋅A F⋅V 
s⋅A 
volt  V  voltage, electrical potential difference, electromotive force  W/A J/C 
kg⋅m^{2}⋅s^{−3}⋅A^{−1} 
farad  F  electrical capacitance  C/V s/Ω 
kg^{−1}⋅m^{−2}⋅s^{4}⋅A^{2} 
ohm  Ω  electrical resistance, impedance, reactance  1/S V/A 
kg⋅m^{2}⋅s^{−3}⋅A^{−2} 
siemens  S  electrical conductance  1/Ω A/V 
kg^{−1}⋅m^{−2}⋅s^{3}⋅A^{2} 
weber  Wb  magnetic flux  J/A T⋅m^{2} 
kg⋅m^{2}⋅s^{−2}⋅A^{−1} 
tesla  T  magnetic field strength, magnetic flux density  V⋅s/m^{2} Wb/m^{2} N/(A⋅m) 
kg⋅s^{−2}⋅A^{−1} 
henry  H  electrical inductance  V⋅s/A Ω⋅s Wb/A 
kg⋅m^{2}⋅s^{−2}⋅A^{−2} 
degree Celsius  °C  temperature relative to 273.15 K  K  K 
lumen  lm  luminous flux  cd⋅sr  cd 
lux  lx  illuminance  lm/m^{2}  m^{−2}⋅cd 
becquerel  Bq  radioactivity (decays per unit time)  1/s  s^{−1} 
gray  Gy  absorbed dose (of ionizing radiation)  J/kg  m^{2}⋅s^{−2} 
sievert  Sv  equivalent dose (of ionizing radiation)  J/kg  m^{2}⋅s^{−2} 
katal  kat  catalytic activity  mol/s  s^{−1}⋅mol 
There is a set of twenty prefixes to the SI unit names and unit symbols that may be used when specifying multiples and fractions of the units. Prefixes are added to unit names to produce multiples and submultiples of the original unit. Below, you can find the list of the SI units prefixes.
Prefix Name  Prefix Symbol  Factor  Decimal 
yotta  Y  10^{24}  1000000000000000000000000 
zetta  Z  10^{21}  1000000000000000000000 
exa  E  10^{18}  1000000000000000000 
peta  P  10^{15}  1000000000000000 
tera  T  10^{12}  1000000000000 
giga  G  10^{9}  1000000000 
mega  M  10^{6}  1000000 
kilo  k  10^{3}  1000 
hecto  h  10^{2}  100 
deca  da  10^{1}  10 
10^{0}  1  
deci  d  10^{−1}  0.1 
centi  c  10^{−2}  0.01 
milli  m  10^{−3}  0.001 
micro  μ  10^{−6}  0.000001 
nano  n  10^{−9}  0.000000001 
pico  p  10^{−12}  0.000000000001 
femto  f  10^{−15}  0.000000000000001 
atto  a  10^{−18}  0.000000000000000001 
zepto  z  10^{−21}  0.000000000000000000001 
yocto  y  10^{−24}  0.000000000000000000000001 
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