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Electronics Engineering Tool

Signal Attenuation Calculator

Calculate signal attenuation in decibels from input and output voltage or power. Convert between dB loss and signal ratios for cables, filters, amplifiers, transmission lines, RF systems, and electronic circuits.

Signal Attenuation Calculator

Choose a calculation mode and enter the known signal values.

Signal Attenuation
6.021 dB
Output / Input
0.5000
Output %
50.00%
Signal Reduction
50.00%
A(dB) = 20 log₁₀(Vin / Vout)
Voltage attenuation assumes the input and output voltages are measured under the same impedance conditions.
INPUT
ATTENUATOR 6.02 dB LOSS
OUTPUT

Signal Attenuation Formulas

Decibels provide a logarithmic way to describe the reduction or increase of a signal. The appropriate equation depends on whether the comparison is based on voltage or power.

Voltage attenuation A = 20 log₁₀(Vin / Vout)
Power attenuation A = 10 log₁₀(Pin / Pout)
Voltage ratio from attenuation Vout/Vin = 10−A/20
Power ratio from attenuation Pout/Pin = 10−A/10

Voltage Attenuation

When comparing voltages under the same impedance conditions, attenuation is calculated with a 20 log₁₀ relationship.

For example, reducing a signal from 1 V to 0.5 V produces approximately 6.02 dB of voltage attenuation.

Power Attenuation

Power ratios use 10 log₁₀ because power is the directly measured quantity in the calculation.

A reduction from 1 W to 0.5 W corresponds to approximately 3.01 dB of power attenuation.

Signal Ratio

An attenuation value can also be converted back into a linear signal ratio.

For voltage, the ratio is 10−dB/20. For power, it is 10−dB/10.

Common Signal Attenuation Values

The following values show how common attenuation levels correspond to voltage and power ratios.

Attenuation Voltage Ratio Voltage Output Power Ratio Power Output
1 dB 0.8913 89.13% 0.7943 79.43%
3 dB 0.7079 70.79% 0.5012 50.12%
6 dB 0.5012 50.12% 0.2512 25.12%
10 dB 0.3162 31.62% 0.1000 10.00%
20 dB 0.1000 10.00% 0.0100 1.00%
30 dB 0.03162 3.162% 0.0010 0.10%
40 dB 0.0100 1.00% 0.0001 0.01%

Worked Examples

Example 1: Voltage Attenuation

Suppose a signal enters a circuit at 2 V and leaves at 1 V.

A = 20 log₁₀(2 / 1)
A ≈ 6.02 dB

The output voltage is 50% of the input voltage, corresponding to approximately 6.02 dB of voltage attenuation.

Example 2: Power Attenuation

A transmission line receives 10 W and delivers 1 W to its load.

A = 10 log₁₀(10 / 1)
A = 10 dB

The output power is one tenth of the input power, so the system has 10 dB of power attenuation.

Where Signal Attenuation Is Used

RF & Wireless

Calculate cable loss, connector loss, transmission-line attenuation and RF signal levels.

Audio Systems

Analyze signal levels through cables, pads, mixers, filters and other audio circuits.

Filters

Express insertion loss and signal reduction at selected frequencies.

Instrumentation

Compare measured input and output levels in electronic test and measurement systems.

Practical Attenuation Design Notes

Equal Impedance Matters

The voltage-to-dB relationship 20 log₁₀(Vin/Vout) directly represents the corresponding power ratio when the input and output measurements use the same impedance.

If impedances differ, voltage ratio and power ratio should not be treated as interchangeable without accounting for the impedance values.

Negative Gain vs. Attenuation

A signal transmission ratio can also be written as a signed gain in dB:

GV = 20 log₁₀(Vout/Vin)
A loss of 6.02 dB corresponds to a signed voltage gain of −6.02 dB.

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Signal Attenuation FAQ

Signal attenuation is the reduction in signal level as a signal passes through a cable, resistor, filter, connector, transmission line, or other circuit. It is commonly expressed in decibels (dB).
For voltage measurements under the same impedance conditions, attenuation in decibels can be calculated as A(dB) = 20 log10(Vin/Vout).
Power attenuation is calculated as A(dB) = 10 log10(Pin/Pout).
When describing signal loss, attenuation is commonly reported as a positive loss value. For example, an output that is half the input voltage corresponds to approximately 6.02 dB of voltage attenuation under equal impedance conditions.
A 3 dB power attenuation means the output power is approximately half the input power. For equal impedances, the corresponding voltage ratio is approximately 0.707.
A 10 dB power attenuation means the output power is one tenth of the input power. For equal impedances, the voltage ratio is approximately 0.316.
Voltage attenuation uses 20 log10 because power is proportional to voltage squared when impedance remains constant. Power attenuation uses 10 log10 directly.
Yes. Attenuation can be much greater than 100 dB in filters, RF systems, shielding measurements, optical systems, and other applications where very large signal reductions are required.