dB Gain Calculator — Decibel Gain & Attenuation
Enter input and output values (voltage, current or power) to calculate gain or attenuation in decibels. The calculator uses the correct factor — 20·log₁₀ for field quantities, 10·log₁₀ for power.
Quantity type
Positive dB = amplification (output > input)
- 1
Linear ratio (out ÷ in)
10 ÷ 1 = 10 - 2
dB gain
20 × log₁₀(10) = 20Factor 20 is used for field quantities (voltage, current).
How does this calculator work?
dB gain = 20 × log₁₀(V_out/V_in) for voltage or current, or 10 × log₁₀(P_out/P_in) for power. Positive dB is amplification, negative is attenuation. +3 dB ≈ doubled power, +6 dB ≈ doubled voltage, +20 dB = voltage × 10. Enter input and output values to get the exact figure.
Formula
How this is calculated
A decibel (dB) is a logarithmic unit that expresses a ratio between two values. Because human perception of sound and many engineering signals is roughly logarithmic, dB compresses a wide dynamic range (factors of millions) into a manageable scale.
For field quantities — voltage and current, which are proportional to the square root of power — the formula uses a factor of 20: dB = 20 × log₁₀(V_out / V_in). For power directly, the factor is 10: dB = 10 × log₁₀(P_out / P_in). Both are consistent because 10 × log₁₀(V²) = 20 × log₁₀(V). A gain of +3 dB means power has doubled (voltage increased by √2 ≈ 1.414); +6 dB means voltage doubled (power quadrupled); +20 dB means voltage is 10× (power is 100×).
Negative dB values indicate attenuation (output is less than input). Zero dB means no change (ratio = 1). The inputs must be in the same units (both in volts, both in mW, etc.) — the absolute unit cancels in the ratio.
Frequently asked questions
Power is proportional to voltage squared (P = V²/R). Because log₁₀(V²) = 2 × log₁₀(V), multiplying by 10 for power is identical to multiplying by 20 for voltage. This keeps dB self-consistent across both representations.
Zero dB means the output equals the input — a unity gain with no amplification or attenuation. Positive dB is a gain; negative dB is a loss.
No. The numerator and denominator must be the same type of quantity in the same units. If you mix voltage and power, the result is meaningless. Select the correct "Quantity type" to apply the right formula.
Also known as
TG we-Calculate Editorial Team. (2026). dB Gain Calculator — Decibel Gain & Attenuation [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/db-gain-calculator
TG we-Calculate Editorial Team. "dB Gain Calculator — Decibel Gain & Attenuation." TG we-Calculate. 2026. https://we-calculate.com/calculator/db-gain-calculator.
TG we-Calculate Editorial Team, "dB Gain Calculator — Decibel Gain & Attenuation," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/db-gain-calculator
@misc{wecalculate_db_gain_calculator, title = {dB Gain Calculator — Decibel Gain & Attenuation}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/db-gain-calculator}}, year = {2026}, note = {TG we-Calculate} }
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