# Equivalent noise resistance

In telecommunication, an equivalent noise resistance is a quantitative representation in resistance units of the spectral density of a noise-voltage generator, given by $R_n = \frac {\pi W_n}{k T_0}$ where $W_n$ is the spectral density, $k$ is the Boltzmann's constant, $T_0$ is the standard noise temperature (290 K), so $kT_0 = 4.00 \times 10^{-21}\,[Ws]$.
$R_n = \frac{e^2}{4 k T_0\,\Delta f}.$