Decibel Ratio Calculator
Convert between a ratio and decibels, for power or amplitude.
Ratios and decibels, both ways
Decibels express ratios on a logarithmic scale, but the formula depends on whether you are dealing with power or amplitude. This calculator converts in both directions for either quantity, so you never apply the wrong factor of 10 or 20.
A power ratio of 2 is about 3.01 dB, while an amplitude ratio of 2 is about 6.02 dB — the same ratio, different decibels. Getting this right matters for audio, RF, and signal work.
Correct and private
It uses 10·log₁₀ for power and 20·log₁₀ for amplitude, converting in your browser with nothing uploaded.
Frequently Asked Questions
Why are power and amplitude different?
Decibels use 10·log₁₀ for power ratios and 20·log₁₀ for amplitude (voltage or pressure) ratios, because power is proportional to amplitude squared.
What does 3 dB mean?
Roughly a doubling of power (a ratio of 2), or a 1.41× amplitude increase. −3 dB is a halving of power.
Can it go both ways?
Yes — enter a ratio to get decibels, or enter decibels to get the ratio, for whichever quantity you select.
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