10Noise power may be calculated using the formula Pn = kTB, where Pn is the noise power in watts, k is Boltzmann’s constant (1.38 × 1023 J/K), T is the absolute temperature in Kelvin, and B is the bandwidth of the noise in Hertz. Noise power usually expressed in units of dBm rather than watts, because typical noise power values for ambient temperatures on Earth are so incredibly small.