Definition of SI base units

International System of Units (SI) International System of Units
A consistent system of units adopted and recommended by the General Conference on Weights and Measures (CGPM) in 1980. Note: SI is the internationally accepted symbol for the International System of Units.
Currently, there are 7 basic units under the International System of Units: Length meter M Mass kilogram (kg) Kg Time second S Current ampere A Thermodynamic temperature Kelvin K Amount of substance mole Mol Luminous intensity candela cd

Definitions of SI base units
Meter: The length of the path travelled by light in a vacuum during a time interval of 1/299792458 s. [17th General Conference on Weights and Measures (1983)]
Kilogram: The mass of the international prototype kilogram. [1st General Conference on Weights and Measures (1889) and 3rd General Conference on Weights and Measures (1901)]
Second: The duration of 9,192,631,770 cycles of radiation corresponding to the transition between two hyperfine levels of the ground state of the caesium-133 atom. [13th General Conference on Weights and Measures (1967), Resolution 1]
Ampere: In a vacuum, if two infinitely long parallel circular straight wires of negligible cross-sectional area and 1 m apart are passed with equal constant currents, and if the mutual force between the wires is 2 × 10-7 N per meter of length, then the current in each wire is 1 A. [CIPM (1946) Resolution 2. [ 9th CGPM (1948)]
Metre: length of the path travelled by light in a vacuum during a time interval of 1/299,792,458 seconds. [17th CGPM (1983)]
Kilogram: mass of the international prototype kilogram. [1st CGPM (1889) and 3rd CGPM (1901)]
Second: duration of 9,192,631,770 cycles of radiation corresponding to the transition between two hyperfine levels of the ground state of the caesium-133 atom. [13th CGPM (1967), resolution 1]
Ampere: in a vacuum, if two infinitely long parallel circular straight wires of negligible cross-sectional area, 1 m apart, are carried by an equal constant current, then the current in each wire is 1 A if the mutual force between the wires is 2 × 10-7 N per metre of length. [CIPM (1946) resolution 2. [9th General Conference on Weights and Measures (1948) approved]
Kelvin: 1/273.16 of the thermodynamic temperature of the triple point
of water. [13th General Conference on Weights and Measures (1967), resolution 4] Mole: The amount of a substance in a system containing as many elementary units (atoms, molecules, ions, electrons and other particles, or a specific combination of these particles) as there are atoms in 0.012 kg of carbon-12. [14th General Conference on Weights and Measures (1971), resolution 3]
Candela: The intensity of light in a given direction from a source emitting monochromatic radiation of a frequency of 540 × 1012 Hz and having an intensity in that direction of (1/683) W/sr. [16th General Conference on Weights and Measures (1979), resolution 3]

Derived units of the International System of Units (SI)

Derived units with special names in the International System of Units
Plane angle radian rad
solid angle steradian sr
frequency hertz Hz
force (gravity, pressure) newton N
pressure (stress) pascal Pa
energy (work, heat) joule J
power (radiant flux) watt W
charge coulomb 0C
potential (voltage, electromotive force) volt V
capacitance farad F
resistance ohm Ω
conductivity siemens S
magnetic flux weber Wb
magnetic flux density magnetic induction tesla TH
inductance henry H Celsius
temperature Celsius 0C
luminous flux lumen lm
illuminance lux lx
radioactivity becquerel Bq
absorbed dose gray Gy
dose equivalent sievert Sv