dB Gain Calculator

How to Use This Calculator

Voltage → dB mode: Enter the input voltage (V_in) and output voltage (V_out) of your amplifier or circuit. The calculator instantly shows the gain in dB and the voltage gain ratio.

dB → Voltage Gain mode: Enter a gain value in decibels to find the corresponding voltage gain ratio (V_out / V_in). Negative dB values indicate signal attenuation rather than amplification.

Both V_in and V_out must be greater than zero in voltage mode. The dB field accepts any real number, including negative values.

Formula

dB — gain in decibels
V_out — output voltage (volts)
V_in — input voltage (volts)
V_out / V_in — dimensionless voltage gain ratio

Example

Frequently Asked Questions

What does a negative dB value mean?
A negative dB value means the output voltage is lower than the input — the circuit is attenuating (reducing) the signal rather than amplifying it. For example, −6 dB corresponds to a voltage gain ratio of about 0.5, meaning the output is half the input.

What is 0 dB gain?
0 dB means V_out equals V_in, so the voltage gain ratio is exactly 1. The signal passes through unchanged in amplitude. This is sometimes called unity gain.

Why use decibels instead of a plain ratio?
Decibels compress a very wide range of gain values into a manageable scale, and they add linearly when cascading stages (where ratios would multiply). A chain of three 6 dB amplifiers gives 18 dB total — simply add the dB figures.

Is this calculator for voltage gain or power gain?
This calculator uses the voltage gain formula (factor of 20). Power gain uses a factor of 10: dB = 10 × log₁₀(P_out / P_in). The two formulas are consistent when the input and output impedances are equal.

What is a typical dB gain for an op-amp amplifier?
Common op-amp stages range from a few dB up to 40–60 dB. An inverting amplifier with a 10 kΩ feedback resistor and a 1 kΩ input resistor has a gain of 10 (20 dB). High-gain RF amplifiers can reach 80 dB or more.