Amplifier Gain (dB) Calculator

Work out amplifier gain (db) instantly with clear inputs, formula shown and shareable results.

About Amplifier Gain (dB) Calculator

Voltage gain in decibels is 20log10 of the voltage ratio; power gain is 10log10 of the power ratio. The two are equal only when input and output impedances match, which is why RF engineers use 10log10 on power and audio engineers 20log10 on voltage.

Formula

Gain in dB

voltage gain = 20 log10(Vout/Vin); power gain = 10 log10(Pout/Pin)

Worked example

With the default values below, Amplifier Gain (dB) Calculator returns Voltage gain of 33.98. Change any input above and every figure here is recalculated in your browser.

Inputs used

Input voltage: 25 mV
Output voltage: 1,250 mV
Input impedance: 50 Ω
Output impedance: 50 Ω

Results

Voltage gain: 33.98 dB
Voltage gain: 50.00 x
Power gain: 33.98 dB
Power gain: 2,500.00 x

Step by step

1Values used
2Gain in dB
3Voltage gain= 33.98 dB
4Voltage gain= 50.00 x
5Power gain= 33.98 dB
6Power gain= 2,500.00 x

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why 20 for voltage and 10 for power?

Power is proportional to voltage squared, and the square becomes a factor of two in front of the logarithm.

When do the two figures differ?

Whenever input and output impedances are unequal. A voltage gain of 50 into a lower impedance gives a different power gain in dB.