dBm to dBu Calculator

This tool converts from dBm to dBu.



???? dBu to dBm


dBu = dBm – 27.78 + 10*Log10(Z)

where Z is the impedance

If the power is specified in Watt, convert the number to dBm first.

Example Calculations

A value of 30 dBm (1 Watt) is equivalent to 19.2 dBu when the impedance is 50 ohm.


What is dBu?

dBu is the RMS voltage relative to 0.7746 Volt.

1 VRMS is therefore equivalent to 20*Log10(1/0.7746) = 2.218 dBu.

The inverse relationship or conversion from dBu to VRMS is defined by the formula VRMS = 10(dBu / 20) x 0.7746.


Where does the number 0.7746 come from?

It is the value of voltage that dissipates 1 milliwatt (mW) into a 600 ohm load. Reference: Wikipedia article on dB Voltage

Image Credit: Omegatron

V = √(600Ω * 0.001W) Volt = 0.7746 V

dBu was originally dBv, however it was changed to what it is today to avoid confusion with dBV. Wikipedia Reference.

What is dBm?

dBm stands for deciBel referenced to 1 milliwatt. It is an absolute unit of power. The following formula is used to convert Watt to dBm:

PdBm = 10*log10(1000*PW)


  • PW is the power expressed in watt.
  • PdBm is the power expressed in dBm