The Basic Fundamental Units Conversion calculaotr provides conversions between many of the commonly used base fundamental units: amount of substance, distance, electric current, intensity of light, mass, temperature, time
The definitions of the international system of units (SI units) has seven fundamental units whose measurements are based on physical descriptions of the units derived from stable, unmodifiable properties of the universe.
The General Conference on Weights and Measures has replaced all but one of the definitions of the base SI units. Efforts continue to create definitions that will not vary over time and can be recreated from fundamental universal constants.
The official definition of each fundamental unit is made official by the International Bureau of Weights and Measures (BIPM)
Amount of Substance - the base unit of amount of substance is the mole. The mole measures the number of atoms or molecules in an object or amount of substance.
The BIPM defines amount of substance by: "The mole is the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of carbon 12."
Distance - the base unit of distance, the meter, is defined by the distance light travels at the speed of light in a vacuum. Since the universal constant speed of light is defined as 299,792,458 meters per second, the distance it travels each second is fixed. The BIPM defines distance by: "The metre is the length of the path traveled by light in vacuum during a time interval of 1/299,792,458 of a second."
Electric Current - the base unit of electric current is the Ampere and represents the current flow of one coulomb of charge per second. The BIPM defines electric current by: "The ampere is that 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 x 10–7 newton per metre of length."
Light Intensity - the base unit of intensity of light is the candela. The candela is defined to be the luminous intensity of a light source producing a single-frequency light at a frequency of 540 terahertz (THz). The BIPM defines light intensity by: "The candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 x 1012 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian."
Mass - the base unit of mass, the kilogram, is still defined as a physical object. The BIPM defines mass by: "The kilogram is the unit of mass; it is equal to the mass of the international prototype of the kilogram."
Today the International Bureau of Weights and Measures (BIPM) stores the world's standard kilogram in Paris. There are effort underway to define the kilogram as a perfect sphere of silicon with diameters approximately 93.6mm. Silicon was chosen because the manufacturing process for creating a silicon ingot has the ability to create defect free silicon and we can then cut a perfectly round sphere to a precise radius thus reproducing the kilogram repeatably.
Temperature - the base unit of temperature is the degree Kelvin (`""^oK`). One kelvin has the same temperature difference as one degree Celsius.
The BIPM defins temperature by: ''The kelvin, unit of thermodynamic temperature, is the fraction 1/273.16 of the thermodynamic temperature of the triple point of water."
Time - the base unit of time, the second, defined as that period of time in which the waves of radiation emitted by cesium atoms, under specified standard conditions, undergo exactly 9,192,631,770 cycles.
The BIPM defines mass by: "The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom."