**Vacuum permittivity is a physical constant that denotes the ideal value of the absolute dielectric permittivity of a classic vacuum.** It is also known as permittivity of free space or electric constant and has a value of roughly 8.854E-12 farads per meter.

Vacuum permittivity connects the concepts of mechanical measurements to that of electric charges. The constant is used in Coulomb's Law to calculate the force experienced by two electric charges that have been separated from each other. As the distance between the two charges increases, the force acting between them decreases. Vacuum permittivity also appears as part of Maxwell's equations that relate magnetic and electric fields to their respective sources.

The value of vacuum permittivity may be calculated from the speed of light and another constant called the permeability of free space. Vacuum permittivity is calculated as the reciprocal of the product of the square of the speed of light and the permeability of free space. The formula for this relationship is e0 = 1 / (c^2 x u0), where "e0" is the vacuum permittivity, "c" is the speed of light and "u0" is the permeability of free space.

The origin of the concept of vacuum permittivity stemmed from experiments by French physicist Charles-Augustin de Coulomb, who developed a working definition of attractive and repulsive electrostatic forces.