Decibel (dB) Gain Calculator

Convert linear power, voltage, and current ratios into logarithmic decibels (dB).

dB Calculator

Enter any 2 values to calculate the 3rd

dB = 10 × log₁₀(P₂/P₁)

Quick Guide

Power vs Voltage/Current dB

Decibels (dB) are used to express the ratio of two values (usually power or root-power) on a logarithmic scale. Because Power is proportional to the square of Voltage $(P = V^2 / R)$, a factor of 2 applies to the logarithm for Voltage and Current, resulting in the $20 \log$ rule instead of the $10 \log$ rule for Power.

Common dB Rules of Thumb:

RatioPower (10log)Voltage (20log)
x 2+3 dB+6 dB
x 10+10 dB+20 dB
/ 2-3 dB-6 dB
/ 10-10 dB-20 dB