# dBm to Vpp Calculator

This tool converts from a dBm (deciBel relative to 1 milliwatt) power value to Vpeak-to-peak or Vpp. It also calculates the RMS voltage.

The default impedance (Z) is 50 ohm, although you can change that to any value.

ðŸ”„ Volt peak-to-peak to dBm

## Formula

Power in Watt (PW) can be converted to RMS voltage (VRMS) using the following formula

VRMS = âˆš(Z*PW)

where Z is the impedance.

As well, PdBm can be converted to PW from:

PW=(10(PdBm/10))/1000

The relationship between VRMS and Power in dBm is therefore given by

VRMS = âˆš(Z/1000)*10(PdBm/20)

The peak-to-peak voltage is given by

Vpp2*Vp

Vpp = (2âˆš2)*VRMS

Substituting for VRMS gives the formula for Vpp from the power in dBm

Vpeak-to-peak = 2*âˆš((2*Z)/1000)*10(PdBm/20)

## Example Calculations

1 dBm into a 50 ohm impedance translates to Vpp of 0.71 Volt. The same power into half the impedance value gives a peak to peak voltage of 0.51 V.

If a circuit requires 0 dBm power into it, then the equivalent voltage is 632 mVpp into 50 Î©.

## Background

### What is peak-to-peak voltage?

Peak to peak voltage or Vpp, as the name suggests, is the difference between the maximum and minimum values of a voltage.

Referring to the picture of a sine wave above, there are three different voltage levels:

1. Peak Voltage (Vp)
2. Peak-to-peak Voltage (Vpp)
3. RMS Voltage (VRMS)

The voltage swing for the perfect sinusoid is symmetric about DC or 0 Volt. Therefore, the negative and positive peak values are the same in magnitude or Vp = u in the figure.

The peak to peak voltage is computed by finding the difference between the crest of the waveform u and the trough -u. Therefore Vpp = 2u

### How to measure Vpp?

In the above example we have calculated Vpp from a visual representation of a sine wave – as seen on an oscilloscope, for example.

Most modern oscilloscopes have built-in mathematical functions to calculate Vpp and other related quantities. In older analog oscilloscopes, this computation required the use of horizontal bars on the screen.

### How to measure dBm?

dBm or signal power can be measured using either a power meter or a spectrum analyzer.

The power meter includes a diode power sensor shown in the picture above that is capable of accurate dBm measurements over a specified range. Exceeding that range even for a brief time period can damage the sensor.

ðŸ’¡ These instruments however do not provide an indication of what the time domain nature of the waveform is. For instance a power meter will not tell you if the input signal is a sine or square wave.

The formulas on this page assume a sine wave to find Vpp from VRMS. The relationship in this case is Vpp = (2âˆš2)*VRMS

If the waveform type is known, then the relationships on this page can be used to calculate Vpp from the RMS voltage instead. For instance, if it’s a square wave then, Vpp = 2*VRMS

### What is Vpp for non-sinusoidal waveforms?

The picture below shows different waveforms. In all cases the peak voltage is the same and therefore Vpp will be the same.

However it is important to note that the power associated with each is different.

The calculator on this page can only be used to convert dBm to Vpp assuming a sine wave.

### Why convert from dBm to Vpp?

RF signal power is typically expressed in dBm. For instance the output of a microwave signal generator. Use the calculator on this page to find the equivalent peak-to-peak voltage. The computation also requires the impedance value.

In general, a dBm to volt conversion implies RMS voltage using the equation: VRMS = âˆš(Z/1000)*10(PdBm/20)