This tool converts from dBm to dBu.

**Formula**

**dBu = dBm – 27.78 + 10*Log _{10}(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.

**Background**

**What is dBu?**

**dBu is the RMS voltage relative to 0.7746 Volt. **

1 V_{RMS} is therefore equivalent to 20*Log_{10}(1/0.7746) = 2.218 dBu.

The inverse relationship or conversion from dBu to V_{RMS} is defined by the formula V_{RMS} = 10^{(dBu / 20)} x 0.7746.

**Notes: **

- dBu is different from dBV which is the RMS voltage relative to 1 Volt.
*dBV to dBm Calculator.* - dBu is also not the same as dBuV or dBµV which is the RMS voltage relative to 1 microvolt.
*dBµV to dBm Calculator.*

**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*

**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:

**P _{dBm} = 10*log_{10}(1000*P_{W})**

where

**P**is the power expressed in watt._{W}**P**is the power expressed in dBm_{dBm}