The phrase "a fundamental quantity" is correct and usable in written English.
It can be used in scientific or mathematical contexts to refer to a basic measurable property or characteristic that is essential to a particular field of study.
Example: "In physics, mass is considered a fundamental quantity that plays a crucial role in understanding the laws of motion."
Alternatives: "a basic measure" or "an essential variable".
This latter number represents a fundamental quantity known as one faraday of electricity.
(The discriminant, familiar to some as the expression "under the square root sign" in the quadratic formula, is a fundamental quantity associated to a polynomial).
The constant of gravitation is plainly a fundamental quantity, since it appears to determine the large-scale structure of the entire universe.
Gravity is a fundamental quantity whether it is an essentially geometric parameter, as in general relativity, or the strength of a field, as in one aspect of a more-general field of unified forces.
The magnetic field is a fundamental quantity in space plasma studies.
In dimensional analysis problems in economics, the dollar is a fundamental quantity.
Indeed, it is difficult to single out a more fundamental quantity causing the differences in degree distributions, as we will see in the rest of this section.
In fields of optics and photonics, the refractive index of a medium is the most fundamental quantity, thus a key material property determining performance in a variety of applications such as antireflection coatings, Bragg reflectors, photovoltaic cells, and light emitters [58, 61 66].
Although river discharge is a fundamental hydrologic quantity, conventional methods of streamgaging are impractical, expensive, and potentially dangerous in remote locations.
Solvation free energy is a fundamental thermodynamic quantity that should be determined to estimate various physicochemical properties of a molecule and the desolvation cost for its binding to macromolecular receptors.
The ion composition of plasma in the magnetosphere and the plasma sheet is one of important parameters in space physics, because it affects the Alfvén velocity that is a fundamental physical quantity of plasma.
