dB Calculator: Power, Voltage and dBm Conversions

Pick a conversion and enter the value. Power ratios use 10 log, voltage ratios 20 log, and dBm is power relative to 1 mW.

Calculator

Gain
20 dB

Type numbers like 4.7, 0.002 or 2e-3. Results are rounded to 4 significant figures.

The formulas

GdB=10log⁡10P2P1GdB=20log⁡10V2V1\begin{gathered} G_{\text{dB}} = 10\log_{10}\dfrac{P_2}{P_1} \\ G_{\text{dB}} = 20\log_{10}\dfrac{V_2}{V_1} \end{gathered}

The voltage form assumes both voltages are across equal resistances.

PdBm=10log⁡10P1 mWP_{\text{dBm}} = 10\log_{10}\dfrac{P}{1\text{ mW}}

0 dBm = 1 mW, 30 dBm = 1 W. Adding gains in dB to a level in dBm gives a level in dBm.

  • A ratio of 2 is about 3.01 dB in power but about 6.02 dB in voltage.

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