The dBm calculator - conversion dBm to volt mW voltage V dB dBu dBV dBm conversion and calculation milliwatt milliwatts kilowatt power level power watts convertor converter audio engineering sound recording

• Conversion: Voltage V to Level dB, dBu, dBV, and dBm •

Usually we measure AC voltage V as volts_RMS.

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The index u at decibel (dB) means unloaded source, V (volt). Some say: The "u" in dBu
implies also that the load impedance is unspecified, or unterminated and is likely to be high.
The index m at dB (decibel) means 1 milliwatt (power) as reference value for 0 dB.

If the reverse conversion dBu, or dBV to volts is needed, go to the converter at the bottom.

• What is dBu?
A logarithmic voltage ratio with a reference voltage of V₀= 0.7746 volt ≡ 0 dBu

• What is dBV?
A logarithmic voltage ratio with a reference voltage of V₀ = 1.0000 volt ≡ 0 dBV
The max. domestic recording level of −10 dBV means 0.3162 volts, that is −7.78 dBu

Level

Voltage

• What is dBm?
A logarithmic ratio with a reference power of P₀ = 1.000 milliwatt ≡ 0 dBm.
The dBm is not used in audio engineering. With the known impedance value you
can convert voltage V to level dBm (power) and vice versa.

For radio frequency systems (RF), impedance matching or power matching
is absolutely essential.

• The dBm calculator for impedance matching
or power matching •

Not used in audio engineering.

Enter two values, the third value will be calculated.
Voltage V, level L, and impedance Z

Voltage V V RMS

Power level L dBm re 1 mW

Impedance Z Ω

dBm indicates that the reference power is P₀ = 1 milliwatt = 0.001 watt ≡ 0 dB

Enter a value in the left or right box. The calculator
works in both directions of the ↔ sign.

Electric power (phone) P:
watts ↔ Electric Power level L_P
dB_m (phone)

Reference power P₀ = 1 milliwatt (mW) = 0.001 W ≡ 0 dB_m

Telephone lines need an input impedance and
an output impedance of 600 ohms for
impedance matching (power matching).

Reference voltage at 600 ohms- 1 mW according to 0 dBm

Reference voltage at 50 Ohm - 1 mW according to 0 dBm

dBu is a voltage standard where "zero" (as in zero dB on your meters) is considered to be
0.775 volts and +4 dBu is therefore 1.23 volts. dBm is a power measurement (the "m" stands
for milliwatts), where +4 also happens to be 1.23 volts if the load impedance is 600 ohms.
In many cases (and this is "old school" audio) a 600 ohm load can be assumed, however,
in modern day interconnects input impedances are usually much higher, which kind of renders
the dBm standard useless. This is one reason why most gear is rated in dBu, or in dBV
(another voltage standard).

Impedance matching Z₂ = Z₁
Transformer matched 600 ohm phone transmission line

Telephone amplifier 1 → Telephone amplifier 2

Source impedance Z₂ = ohms | Load impedance Z₁ = ohms

Voltage damping by load Δ L = dB

Damping factor D_F = = R_a / R_i

• Definition of dBm

dBm is defined as power ratio in decibel (dB) referenced to one milliwatt (mW). It is an
abbreviation for dB with respect to 1 mW and the "m" in dBm stands for milliwatt.

dBm is different from dB. dBm represents absolute power, whereas in audio engineering the
decibel is usually a voltage ratio of two values and is used then to represent gain or attenuation
of an audio amplifier, or an audio damping pad.

If you use modern audio equipment in sound engineering, above calculators used at
typically 600 ohms impedance for telephone lines or antennas, are of no value.
Matching impedance for power is not used anymore in the audio field.
You will only use voltage bridging or impedance bridging Z_load >> Z_source.

Here comes your adequate calculator for audio voltage and voltage levels:

Converter: Decibel to Voltage and vice versa
Measurement of input impedance and output impedance

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Electric power (phone) P: watts	↔	Electric Power level L_P dB_m (phone)

Reference power P₀ = 1 milliwatt (mW) = 0.001 W ≡ 0 dB_m