Electronics Calculator

Voltage ↔ dB Calculator

Convert a voltage ratio to decibels or convert decibels back to a voltage ratio. This calculator uses dB = 20 log10(V2/V1) and is useful for amplifiers, attenuators, audio circuits, RF systems, filters and signal analysis.

Input or reference voltage.
Output or final voltage.
dB
Positive dB means voltage gain; negative dB means voltage attenuation.
Used to calculate an actual output voltage.
Voltage gain
+6.02 dB
A voltage ratio of 2.000 corresponds to approximately +6.02 dB.
Voltage Ratio
2.000 ×
Power Ratio*
4.000 ×
Reference
1.000 V
Output
2.000 V
* Power ratio is derived from the voltage ratio assuming equal impedance.

What is voltage in dB?

Decibels are commonly used to express signal gain or attenuation. When comparing voltages under the same impedance conditions, the voltage ratio is converted to dB using a factor of 20:

dB = 20 log10(V2 / V1)
V1 = reference voltage, V2 = output voltage

Convert dB back to voltage ratio

If the dB value is known, the corresponding voltage ratio can be calculated by reversing the logarithmic equation:

V2 / V1 = 10dB / 20
Positive dB produces a ratio above 1; negative dB produces a ratio below 1.

How the Voltage ↔ dB Calculation Works

Voltage gain and attenuation can be represented logarithmically using decibels. This makes it convenient to describe very small or very large signal changes in amplifiers, filters, cables and RF systems.

1. Find the voltage ratio

Divide the output voltage by the reference voltage:

Ratio = V2 / V1

A ratio greater than 1 represents voltage gain. A ratio below 1 represents attenuation.

2. Convert the ratio to dB

Apply the base-10 logarithm and multiply by 20:

dB = 20 log10(Ratio)

The logarithmic scale makes signal gain and loss easier to compare and combine.

3. Reverse the calculation

To recover the voltage ratio from dB:

Ratio = 10dB/20

Multiply this ratio by the reference voltage to obtain the corresponding output voltage.

Common Voltage dB Values

These values are useful as quick references when working with amplifiers, attenuators and signal levels.

dB Voltage Ratio Approx. Percentage Meaning
+20 dB 10.000 × 1000% 10× voltage gain
+10 dB 3.162 × 316.2% Voltage gain
+6 dB 1.995 × 199.5% Approximately 2× voltage
+3 dB 1.413 × 141.3% Approximately 1.41× voltage
0 dB 1.000 × 100% No voltage change
-3 dB 0.708 × 70.8% Voltage attenuation
-6 dB 0.501 × 50.1% Approximately half the voltage
-10 dB 0.316 × 31.6% Voltage attenuation
-20 dB 0.100 × 10% One-tenth the voltage

Worked Examples

Example 1: Voltage Doubled

A circuit increases a 1 V signal to 2 V.

20 log10(2/1)

Result: +6.02 dB

Example 2: 10× Voltage Gain

An amplifier produces 10 V from a 1 V reference.

20 log10(10)

Result: +20 dB

Example 3: Half Voltage

An attenuator reduces a 2 V signal to 1 V.

20 log10(1/2)

Result: -6.02 dB

Important impedance assumption
The formula 20 log10(V2/V1) represents a voltage ratio in dB when the compared voltages are associated with the same impedance conditions. If the impedances are different, voltage ratio and power ratio are not interchangeable without accounting for impedance.

Voltage dB in Electronics

Audio

Audio amplifiers, preamps, mixers and equalizers often describe voltage gain or attenuation using decibels.

RF

RF systems use dB to describe amplifier gain, cable attenuation, filter response and signal levels.

Filters

Frequency-response plots commonly show gain or attenuation in dB across the operating bandwidth.

Amplifiers

Amplifier stages can be analyzed by converting their voltage gain into logarithmic dB units.

Voltage dB vs Power dB

Voltage Ratio

dB = 20 log10(V2/V1)

The 20 multiplier is used for voltage and current ratios when the relevant impedance conditions allow the voltage relationship to represent the corresponding power relationship.

Power Ratio

dB = 10 log10(P2/P1)

Power ratios use 10 log10. For equal impedances, a voltage ratio can be converted to its corresponding power ratio by squaring the voltage ratio.

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Frequently Asked Questions

For voltages measured across the same impedance, use dB = 20 × log10(V2/V1). V2 is the output or final voltage and V1 is the reference or input voltage.

For a voltage ratio, use V2/V1 = 10^(dB/20). A positive dB value represents a voltage ratio greater than 1, while a negative value represents a ratio below 1.

Voltage dB uses 20 log10 because electrical power is proportional to voltage squared when impedance is constant. Since power uses 10 log10, the voltage expression becomes 20 log10.

0 dB corresponds to a voltage ratio of 1. The output voltage is equal to the reference voltage.

+6 dB corresponds to a voltage ratio of approximately 2.0. More precisely, 10^(6/20) is about 1.995.

-3 dB corresponds to a voltage ratio of approximately 0.708. The output voltage is about 70.8% of the reference voltage.

+20 dB corresponds to a voltage ratio of 10. The output voltage is ten times the reference voltage.

The 20 log10 voltage formula assumes the two voltages are measured across the same impedance, or that the impedance condition makes the voltage comparison appropriate. If impedances differ, power ratios should be considered using the relevant impedances.

dB describes a ratio between two quantities, while dBm describes an absolute power level referenced to 1 mW. A voltage ratio in dB does not by itself specify an absolute power level.