Equivalent NoiseResistor (ENR) is a quantifiable resistance value that corresponds to the spectral density of a noise generator
. Equivalent noise resistance is a relative quantity used as a comparison value with the noise of a resistor. Each resistor produces a thermal noise voltage that is a function of the spectral density, Boltzmann's constant, and absolute temperature in Kelvin. The ENR value is expressed in ohms and is calculated by multiplying pi times the spectral density times Boltzmann's constant times the absolute temperature.