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)

Variables:

  • 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)


FAQ

What is RMS Voltage?

RMS (Root Mean Square) Voltage is a measure of the effective voltage level. It represents the equivalent steady DC (Direct Current) value which gives the same power transfer as the given AC (Alternating Current) voltage. RMS Voltage is crucial in electrical engineering for designing and analyzing circuits that operate with alternating current.

Why is impedance important in calculating RMS Voltage from dBm?

Impedance, measured in ohms, represents the total resistance to the flow of current in a circuit, including both the resistive and reactive components. It’s important in calculating RMS Voltage from dBm because it affects how much voltage is required to achieve a certain power level in a circuit. The impedance essentially dictates how the voltage will be transformed into power, making it a critical factor in the calculation.

How does the dBm value influence the RMS Voltage calculation?

dBm is a logarithmic unit that measures power relative to 1 milliwatt. In the context of calculating RMS Voltage, the dBm value represents the power level that needs to be converted into a voltage level. Since the formula involves 10 raised to the power of dBm/20, higher dBm values will result in a higher calculated RMS Voltage. This reflects the logarithmic relationship between power and voltage, where a small increase in dBm can result in a significant increase in voltage.