Decibel (dB) Calculator

About this tool

Convert between a plain ratio and decibels, for either power ratios (10·log₁₀) or voltage/amplitude ratios (20·log₁₀) — the two most common decibel conventions used in audio, RF, and signal processing.

Frequently asked questions

Why does power use 10·log₁₀ but voltage uses 20·log₁₀?

Power is proportional to voltage squared (P = V²/R), so a voltage ratio squared becomes a power ratio — the extra factor of 2 in the voltage formula (20 instead of 10) accounts for that squaring, keeping both conventions consistent with each other for the same underlying signal.

What does a negative dB value mean?

It means the ratio is less than 1 — a decrease or attenuation rather than a gain. For example, −3dB in power terms corresponds to a ratio of about 0.5 (half the power).

What's a quick reference for common dB values?

+3dB ≈ doubling of power (×1.41 in voltage), +6dB ≈ doubling of voltage (×4 in power), +10dB = ×10 power, +20dB = ×10 voltage (×100 power).