Power Ratio to Decibels Converter
Convert a positive power ratio to decibels using the logarithmic decibel scale. A ratio of one corresponds to 0 dB, while ratios above one produce positive values.
How to use this calculator
- Enter the output-to-input power ratio as a positive number. For example, use 0.1 for one tenth of the reference power.
- Check the labels and units before applying the result to a real task.
- Change one input at a time when comparing scenarios.
Formula and method
dB = 10 log₁₀(Pout/Pin)
- dB = 10 log₁₀(Pout/Pin)
- This is the power-ratio definition. Voltage and amplitude ratios use 20 log₁₀ only under compatible reference and impedance assumptions.
Worked examples
Worked example
A power ratio of 1,000.
10 log₁₀(1,000) = 30 dB.
10 log₁₀(1,000) = 30 dB.
Understanding the result
Convert a positive power ratio to decibels using the logarithmic decibel scale. A ratio of one corresponds to 0 dB, while ratios above one produce positive values.
This is the power-ratio definition. Voltage and amplitude ratios use 20 log₁₀ only under compatible reference and impedance assumptions.
Important notes
This is the power-ratio definition. Voltage and amplitude ratios use 20 log₁₀ only under compatible reference and impedance assumptions.
Displayed values are rounded for readability; retain appropriate precision when continuing a calculation.
Frequently asked questions
What does 0 dB mean?
It means the compared power ratio is one: the output and reference powers are equal.
Can decibels be negative?
Yes. A power ratio between zero and one produces a negative decibel value, indicating less power than the reference.
Can I use 10 log for voltage?
Not directly in general. Voltage-ratio decibels use 20 log when the reference impedances are compatible; different impedances require care.
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Learn the method behind the number or compare the terminology before using the calculator.
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This page provides a calculation tool plus explanatory information so you can understand what the result means and when the underlying method may not fit your situation.