dBV to dBm Calculator

This tool converts from dBV/dBmV/dBuV/dBnV to dBm and Watt

Enter the dBV value and also the impedance (Z). The default value of resistance is 50 ohm but it can be changed to any real number value.

🔄 dBm to dBV

Formula

dBm = dBV − 10*Log10(Z) + 30

where Z is the impedance

Background

What is dBm?

dBm stands for deciBel referenced to one milliwatt.

It is commonly used by RF engineers in the context of absolute power levels associated with various components such as filters, amplifiers, splitters and more.

Mathematically it is defined as

PdBm = 10*log10(PmW)

where

  • PmW is the power expressed in milliwatt.
  • PdBm is the power expressed in dBm

Watt is a unit of power or radiant flux. It is equivalent to 1 joule per second or 1 kg⋅m2⋅s−3. 1 milliwatt is equivalent to 1/1000 Watt or 0.001 Watt.

Note: Watt is a unit of power in the International System of Units (SI). dBm however is not in the International System of Units.

What is dBV?

dBV stands for deciBel relative to 1 Volt.

Mathematically it is expressed as: dBV = 20*Log10(VRMS/1V)

Note: this is 1 Volt RMS (Root-mean-square*) and not average, peak or peak-to-peak.

Using the formula above or the V to dBV converter: 1 Volt is equivalent to 0 dBV and 2 Volt is equivalent to 6.02 dBV.

Based on the definition of RMS voltage below, we can see that it is a positive quantity greater than or equal to zero.

VRMS = √(1/n)(V12 +V22 + … + Vn2)

For values of 

  • VRMS > 1, the equivalent value of dBV will be positive 
  • VRMS < 1, the equivalent dBV will be negative.

The exception is VRMS = 0 where the equivalent dBV is infinitesimally small or -∞.

Note: there is no reliance on impedance or resistance in the V to dBV conversion formula.

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