Thermal Noise & Noise Figure Calculator

Every resistor at a temperature above absolute zero generates noise — the Johnson–Nyquist noise discovered experimentally by Johnson and explained by Nyquist in 1928. The available noise power from any matched source is N = kTB: Boltzmann's constant, absolute temperature, and bandwidth. Nothing about the resistor's value appears — only how hot it is and how much bandwidth you accept.

At the standard reference temperature T₀ = 290 K, the noise power spectral density kT₀ is −174 dBm/Hz — the single most-quoted number in receiver design. Every doubling of bandwidth adds 3 dB: a 1 MHz receiver channel starts from −114 dBm before the receiver's own noise is counted.

The receiver's own contribution is captured by its noise figure NF, defined at the 290 K reference (Friis, 1944). The input-referred noise floor is then kT₀B in dBm plus NF — the level a signal must exceed by the required SNR for the link to work. The same information can be expressed as an equivalent noise temperature Tₑ = T₀(F − 1), the form preferred for satellite receivers where noise figures are fractions of a dB.

This calculator evaluates all four quantities and shows how they connect, so a bandwidth, a temperature, and a noise figure turn into the one number a link budget needs: the noise floor.