MAXScanner engineering calculator
Updated 2026-09-18
Decibel Gain Calculator — Voltage, Power, Ratio & Reverse dB
Convert voltage/amplitude or power ratios to decibels and reverse any positive, zero or negative dB value back to its linear ratio.
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Your calculation, step by step
These steps substitute the values entered above so you can independently check the result.
- 1.Linear ratio: output ÷ input = 2 ÷ 1 = 2×.
- 2.dB = 20 × log10(2) = 6.0206 dB.
- 3.Percent of reference: 200%; gain.
Formula, example and limits
Amplitude dB=20log10(Aout/Ain); power dB=10log10(Pout/Pin); inverse ratio=10^(dB/20 or dB/10).
A voltage ratio of 2 is about +6.0206 dB; a power ratio of 2 is about +3.0103 dB.
- Input and output quantities use the same units.
- The 20log amplitude rule assumes the compared amplitude quantities relate to power under equivalent impedance conditions.
Frequently asked questions
Why does voltage use 20 log but power uses 10 log?
Power is proportional to the square of voltage under the same impedance, so the logarithm introduces the factor of two.
Can gain be negative dB?
Yes. A ratio below one is attenuation and produces a negative dB result.
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