This tool converts from dBm (dB-milliwatt) to dBV (dB-Volt).
Calculator
Note:
- The default impedance is 50 ohm although it can be changed to any value.
- Volt is a Root-mean-square (RMS) quantity
Formula
dBV = dBm + 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
People often confuse dBm with dB. dB or deciBel has no units and represents the logarithm of a power or amplitude ratio. This post explains the relationship between dBm and dB and here’s when the calculation makes sense.
Watt is a unit of power or radiant flux. It is equivalent to 1 joule per second or 1 kg⋅m2⋅s−3
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 greater than 1, the equivalent value of dBV will be positive. If VRMS is less than 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 conversion formula.