International System of Units

Table columns:
Unit name
Unit symbol
Quantity name
Definition (incomplete)[n 1]
Dimension symbol

Table rows:
cells: metre
m
length
Original (1793): 1/10000000 of the meridian through Paris between the North Pole and the Equator.FG Interim (1960): 1650763.73 wavelengths in a vacuum of the radiation corresponding to the transition between the 2p10 and 5d5 quantum levels of the krypton-86 atom. Current (1983): The distance travelled by light in a vacuum in 1/299792458 second.
L
cells: kilogram[n 2]
kg
mass
Original (1793): The grave was defined as being the weight [mass] of one cubic decimetre of pure water at its freezing point.FG Current (1889): The mass of the International Prototype Kilogram (Le Grand K).[39]
M
cells: second
s
time
Original (Medieval): 1/86400 of a day. Interim (1956): 1/31556925.9747 of the tropical year for 1900 January 0 at 12 hours ephemeris time. Current (1967): The duration of 9192631770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom.
T
cells: ampere
A
electric current
Original (1881): A tenth of the electromagnetic CGS unit of current. The [CGS] electromagnetic unit of current is that current, flowing in an arc 1 cm long of a circle 1 cm in radius, that creates a field of one oersted at the centre.[40] IEC Current (1946): The constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 m apart in vacuum, would produce between these conductors a force equal to 2×10−7 newtons per metre of length.
I
cells: kelvin
K
thermodynamic temperature
Original (1743): The centigrade scale is obtained by assigning 0 °C to the freezing point of water and 100 °C to the boiling point of water. Interim (1954): The triple point of water (0.01 °C) defined to be exactly 273.16 K.[n 3] Current (1967): 1/273.16 of the thermodynamic temperature of the triple point of water
Θ
cells: mole
mol
amount of substance
Original (1900): The molecular weight of a substance in mass grams.ICAW Current (1967): The amount of substance of a system which contains as many elementary entities[n 4] as there are atoms in 0.012 kilogram of carbon-12.
N
cells: candela
cd
luminous intensity
Original (1946): The value of the new candle is such that the brightness of the full radiator at the temperature of solidification of platinum is 60 new candles per square centimetre. Current (1979): The luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 5.4×1014 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian.
J
cells: Note Jump up ^ Interim definitions are given here only when there has been a significant difference in the definition. Jump up ^ Despite the prefix "kilo-", the kilogram is the base unit of mass. The kilogram, not the gram, is used in the definitions of derived units. Nonetheless, units of mass are named as if the gram were the base unit. Jump up ^ In 1954 the unit of thermodynamic temperature was known as the "degree Kelvin" (symbol °K; "Kelvin" spelt with an upper-case "K"). It was renamed the "kelvin" (symbol "K"; "kelvin" spelt with a lower case "k") in 1967. Jump up ^ 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. The original definitions of the various base units in the above table were made by the following authorities: FG = French Government IEC = International Electrotechnical Commission ICAW = International Committee on Atomic Weights All other definitions result from resolutions by either CGPM or the CIPM and are catalogued in the SI Brochure.
Note Jump up ^ Interim definitions are given here only when there has been a significant difference in the definition. Jump up ^ Despite the prefix "kilo-", the kilogram is the base unit of mass. The kilogram, not the gram, is used in the definitions of derived units. Nonetheless, units of mass are named as if the gram were the base unit. Jump up ^ In 1954 the unit of thermodynamic temperature was known as the "degree Kelvin" (symbol °K; "Kelvin" spelt with an upper-case "K"). It was renamed the "kelvin" (symbol "K"; "kelvin" spelt with a lower case "k") in 1967. Jump up ^ 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. The original definitions of the various base units in the above table were made by the following authorities: FG = French Government IEC = International Electrotechnical Commission ICAW = International Committee on Atomic Weights All other definitions result from resolutions by either CGPM or the CIPM and are catalogued in the SI Brochure.
Note Jump up ^ Interim definitions are given here only when there has been a significant difference in the definition. Jump up ^ Despite the prefix "kilo-", the kilogram is the base unit of mass. The kilogram, not the gram, is used in the definitions of derived units. Nonetheless, units of mass are named as if the gram were the base unit. Jump up ^ In 1954 the unit of thermodynamic temperature was known as the "degree Kelvin" (symbol °K; "Kelvin" spelt with an upper-case "K"). It was renamed the "kelvin" (symbol "K"; "kelvin" spelt with a lower case "k") in 1967. Jump up ^ 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. The original definitions of the various base units in the above table were made by the following authorities: FG = French Government IEC = International Electrotechnical Commission ICAW = International Committee on Atomic Weights All other definitions result from resolutions by either CGPM or the CIPM and are catalogued in the SI Brochure.
Note Jump up ^ Interim definitions are given here only when there has been a significant difference in the definition. Jump up ^ Despite the prefix "kilo-", the kilogram is the base unit of mass. The kilogram, not the gram, is used in the definitions of derived units. Nonetheless, units of mass are named as if the gram were the base unit. Jump up ^ In 1954 the unit of thermodynamic temperature was known as the "degree Kelvin" (symbol °K; "Kelvin" spelt with an upper-case "K"). It was renamed the "kelvin" (symbol "K"; "kelvin" spelt with a lower case "k") in 1967. Jump up ^ 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. The original definitions of the various base units in the above table were made by the following authorities: FG = French Government IEC = International Electrotechnical Commission ICAW = International Committee on Atomic Weights All other definitions result from resolutions by either CGPM or the CIPM and are catalogued in the SI Brochure.
Note Jump up ^ Interim definitions are given here only when there has been a significant difference in the definition. Jump up ^ Despite the prefix "kilo-", the kilogram is the base unit of mass. The kilogram, not the gram, is used in the definitions of derived units. Nonetheless, units of mass are named as if the gram were the base unit. Jump up ^ In 1954 the unit of thermodynamic temperature was known as the "degree Kelvin" (symbol °K; "Kelvin" spelt with an upper-case "K"). It was renamed the "kelvin" (symbol "K"; "kelvin" spelt with a lower case "k") in 1967. Jump up ^ 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. The original definitions of the various base units in the above table were made by the following authorities: FG = French Government IEC = International Electrotechnical Commission ICAW = International Committee on Atomic Weights All other definitions result from resolutions by either CGPM or the CIPM and are catalogued in the SI Brochure.

Questions about this table:
originalText: what is the standard unit of length in the si system
answer: answerTexts: metre