Decibel (dB) Calculator
The decibel (dB) is the standard unit used throughout amateur radio, RF engineering, telecommunications, and electronics to describe signal gain and loss. This calculator allows you to compare either power or voltage levels and automatically determine the difference in decibels.
Power ratios use a multiplier of 10. Voltage ratios use a multiplier of 20 because electrical power is proportional to the square of voltage — squaring the voltage ratio is equivalent to doubling the logarithmic multiplier.
| Change | dB |
|---|---|
| Double Power | +3 dB |
| Half Power | −3 dB |
| Ten Times Power | +10 dB |
| One-Tenth Power | −10 dB |
| Double Voltage | +6 dB |
| Half Voltage | −6 dB |
- +3 dB is approximately double the power.
- +10 dB is approximately ten times the power.
- −3 dB is approximately half the power.
Small dB changes can represent significant differences in signal performance.
A transmitter increases from 50 watts to 100 watts.
+3 dB
A coax feedline loses half the transmitter power.
−3 dB
An amplifier increases output from 10 watts to 100 watts.
+10 dB
A preamplifier doubles signal voltage.
+6 dB