Calculators

Decibel Calculator

Calculate decibels from power or voltage ratios using 10 × log10 or 20 × log10 formulas locally in your browser.

Calculate decibels from power or voltage ratios. All calculations run locally in your browser.

Enter the measured power in watts. Zero or positive values only.

Enter the reference power in watts. Must be greater than zero.

Your decibel result will appear here.

Convert power or voltage ratios to decibels.

Choose Power mode for 10 × log10(P / Pref) or Voltage mode for 20 × log10(V / Vref). Enter the measured value and reference value in the same units. Power mode is used for power, intensity, and energy ratios. Voltage mode is used for voltage, current, and sound pressure ratios where power is proportional to the square of the quantity. A ratio of 1 gives 0 dB; a ratio of 10 gives 10 dB in power mode or 20 dB in voltage mode; a ratio of 0.1 gives -10 dB or -20 dB respectively. Zero input yields -∞ dB. All calculations run locally in your browser; your values are not uploaded or stored.

Frequently Asked Questions

Everything you need to know about this tool, how it works, and privacy.

When should I use power mode versus voltage mode?

Use Power mode for power, intensity, and energy ratios where the quantity is directly proportional to power. Use Voltage mode for voltage, current, and sound pressure ratios where power is proportional to the square of the quantity. For example, amplifier power gain uses power mode; amplifier voltage gain uses voltage mode.

What does 0 dB mean?

0 dB means the measured value equals the reference value (ratio of 1). Positive dB means the measured value is greater than the reference; negative dB means it is smaller.

Why does a voltage ratio of 10 give 20 dB but a power ratio of 10 gives 10 dB?

Power is proportional to voltage squared. A voltage ratio of 10 means a power ratio of 100, and 10 × log10(100) = 20 dB. The 20 × log10 voltage formula accounts for this squaring relationship.

What happens when the measured value is zero?

The ratio is zero, and log10(0) is negative infinity. The calculator reports -∞ dB, which is the correct mathematical result for a zero signal compared to a non-zero reference.

Do my values stay private?

Yes. The calculation and copy action run locally in your browser. CodeASystem does not upload or store the values you enter.