When do I use 10·log versus 20·log?

Use 10·log₁₀(P/P0) for power ratios. Use 20·log₁₀(A/A0) for amplitude quantities like voltage, current or sound pressure, because power is proportional to amplitude squared.

What does a negative dB value mean?

A negative result means the measured value is smaller than the reference — an attenuation or loss rather than a gain.

Is anything uploaded?

No — every calculation runs locally in your browser, with no network requests.

Decibel (dB) Calculator

Convert a power or amplitude ratio to decibels.

Decibel (dB) calculator

A decibel expresses a ratio on a logarithmic scale. The factor depends on the quantity:

Power: dB = 10 · log₁₀(P / P₀)
Amplitude (voltage, current, sound pressure): dB = 20 · log₁₀(A / A₀)

The amplitude form uses 20 because power is proportional to amplitude squared. Enter your reference and measured values and the dB result updates instantly — all in your browser.