The International System of Units (SI) has seven base units, which are used to measure seven fundamental physical quantities. These base SI units provide the foundation for measuring all other physical quantities. Here are the seven base SI units:

Meter (m): The meter is the base unit of length. It is defined as the distance traveled by light in a vacuum during a time interval of 1/299,792,458 of a second.

Kilogram (kg): The kilogram is the base unit of mass. It is defined as the mass of the international prototype of the kilogram, a platinum-iridium alloy cylinder kept at the International Bureau of Weights and Measures in France.

Second (s): The second is the base unit of time. It is defined as the duration of 9,192,631,770 periods of the radiation corresponding to the transition between two hyperfine levels of the ground state of the cesium-133 atom.

Ampere (A): The ampere is the base unit of electric current. It is defined as the constant current that, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 meter apart in a vacuum, would produce a force between the conductors equal to 2 x 10^(-7) newton per meter of length.

Kelvin (K): The kelvin is the base unit of temperature. It is defined as the fraction 1/273.16 of the thermodynamic temperature of the triple point of water.

Mole (mol): The mole is the base unit of amount of substance. It is defined as the amount of substance of a system that contains as many elementary entities as there are atoms in 0.012 kilograms of carbon-12.

Candela (cd): The candela is the base unit of luminous intensity. It is defined as the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 x 10^12 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian.

These base SI units provide a consistent and standardized way of measuring physical quantities across different fields of science, engineering, and commerce.

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