Sound · decibel conversion
dB to ratio converter.
Turn a gain in dB into how many times the power or the voltage changes, or turn a ratio back into dB. Power uses 10 log, voltage and sound pressure use 20 log.
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Power ratio versus voltage ratio
A decibel compares two quantities on a log scale. For power or intensity the level change is 10 x log10 (P2 / P1). For voltage, current or sound pressure, which are field quantities whose square is proportional to power, it is 20 x log10 (V2 / V1). Wikipedia's Decibel article gives both forms, and HyperPhysics explains the factor of 10.
Worked example. +6 dB is a voltage ratio of 2 (voltage nearly doubles) but a power ratio of 3.98. A 100 times power increase is 20 dB; a 10 times voltage increase is 20 dB.
| Gain | Power ratio | Voltage ratio |
|---|---|---|
| 1 dB | 1.26 | 1.12 |
| 3 dB | 2 | 1.41 |
| 6 dB | 3.98 | 2 |
| 10 dB | 10 | 3.16 |
| 20 dB | 100 | 10 |
Pick the right row: amplifier power gain uses the power column, microphone or line-level voltage gain and sound pressure level use the voltage column.
Frequently asked questions
How many dB is double the power?
About 3.01 dB. Doubling the voltage or sound pressure is about 6.02 dB.
Why is the voltage formula 20 log instead of 10 log?
Power is proportional to voltage squared, and the logarithm of a square is twice the logarithm, so the multiplier doubles from 10 to 20.
Is sound pressure level a power or a voltage ratio?
Sound pressure is a field quantity, so a change in sound pressure level uses 20 log. Sound intensity and sound power use 10 log.
What does a negative dB value mean?
A reduction. For example -6 dB is a voltage ratio of 0.5, about half.
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Mathematical conversion only. Absolute levels such as dBu, dBV or dB SPL need a reference value that this page does not add.