Enter the impedance (ohms) and the dBm into the calculator to determine the RMS Voltage from dBm. 

RMS Voltage from dBm Formula

The following formula is used to calculate the RMS Voltage from dBm. 

Vrms = SQRT( Z/1000) * 10 ^ (dBm/20)


  • Where Vrms is the RMS Voltage from dBm (volts)
  • Z is the impedance (ohms) 
  • dBm is the dBm 

To calculate the RMS voltage from dBm, take the square root of the impedance over 1000, then multiply by 10 to the power of the dBm over 20.

How to Calculate RMS Voltage from dBm?

The following two example problems outline how to calculate the RMS Voltage from dBm.

Example Problem #1:

  1. First, determine the impedance (ohms). In this example, the impedance (ohms) is measured to be 5000.
  2. Next, determine the dBm. For this problem, the dBm is calculated to be 30.
  3. Finally, calculate the RMS Voltage from dBm using the formula above: 

Vrms = SQRT( Z/1000) * 10 ^ (dBm/20)

Inserting the values from above and solving the equation with the imputed values gives: 

Vrms = SQRT( 5000/1000) * 10 ^ (30/20) = 70.71 (volts)

Example Problem #2: 

Using the same process as example problem 1, we first define the variables outlined by the formula. In this case, the values are:

impedance (ohms) = 6000

dBm = 20

Entering these values into the formula or calculator above gives us:: 

Vrms = SQRT( 6000/1000) * 10 ^ (20/20) = 24.494 (volts)