dBm/Hz to Watt and Watt/Hz

This tool converts dBm (deciBel referenced to 1 mW) to Watt and Watt/Hz.


  • Power (dBm) and
  • Bandwidth over which the power is to be integrated (Hz/kHz/MHz/GHz)

What is dBm/Hz used for?

dBm/Hz is the power of the signal measured in a 1 Hz resolution bandwidth.

This unit is often used to specify the sensitivity of a radio receiver or spectrum analyzer. It is referred to as Displayed Average Noise Level (DANL).

The lower the DANL, the more sensitive the analyzer. The lowest noise floor that can be theoretically measured at 0oC is -174 dBm/Hz. This assumes a noise figure of 0 dB.

As the Resolution Bandwidth (RBW) setting of the analyzer is increased, the DANL increases and this tool can be used to calculate that level in Watt.

What does Watt/Hz mean?

Watt is a unit of power and Hz is a unit of frequency.

Watt cannot be converted to Hz and therefore there is no equivalence. This is unlike Hz and kHz for instance where 1000 Hz is equivalent to 1 kHz and one can be converted to another.

Watt/Hz is the amount of energy in one Hz of bandwidth. This can be understood by looking at the Fast Fourier Transform (FFT) of a time domain waveform shown below.

At any specific frequency, the Power integrated over a 1 Hz bandwidth has units Watt/Hz.

In the above example the noise is not flat and therefore we cannot simply multiply the Watt/Hz number by 1000 for instance, to calculate Watt/kHz.

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