Decibel (dB) to Ratio Converter

Enter a decibel (dB) value and get back both the power ratio and voltage ratio — or flip it around and enter a ratio to find the equivalent dB. The Decibel (dB) to Ratio Converter handles both directions using the standard logarithmic formulas: Power Ratio = 10^(dB/10) and Voltage Ratio = 10^(dB/20). Supports positive and negative dB values for gain and loss calculations.

dB

Enter a positive value for gain or negative for loss.

Enter the power ratio to convert to dB. Used when converting Ratio → dB.

Power ratio uses ×10; voltage ratio uses ×20.

Results

Power Ratio

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Voltage Ratio

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Equivalent dB (from Ratio)

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Equivalent dB — Voltage (from Ratio)

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Power Ratio vs Voltage Ratio

Results Table

Frequently Asked Questions

What is a decibel (dB)?

A decibel is a logarithmic unit used to express the ratio of two quantities, typically power or intensity levels. It is widely used in acoustics, electronics, and telecommunications because it compresses very large or very small ratios into a manageable scale. Decibels express how many times more (positive dB) or less (negative dB) a value is relative to a reference — but not the absolute amount.

What is the formula to convert dB to power ratio?

The power ratio is calculated as: Power Ratio = 10^(dB / 10). For example, 20 dB corresponds to a power ratio of 10^(20/10) = 100, meaning the output power is 100 times the input power.

What is the formula to convert dB to voltage ratio?

The voltage ratio is calculated as: Voltage Ratio = 10^(dB / 20). For 20 dB, the voltage ratio is 10^(20/20) = 10. Note that voltage ratio equations are only strictly valid when both voltages appear across equal impedances.

Why does power use 10×log and voltage use 20×log?

Because power is proportional to the square of voltage (P = V²/R). Taking the square root relationship into account means the dB scale for voltage must use a factor of 20 (which is 2 × 10) instead of 10 to remain consistent with the power-based definition of decibels.

How do I convert a power ratio back to dB?

Use the formula: dB = 10 × log₁₀(Power Ratio). For a power ratio of 100, dB = 10 × log₁₀(100) = 10 × 2 = 20 dB. For a voltage ratio back to dB, use: dB = 20 × log₁₀(Voltage Ratio).

What does a negative dB value mean?

A negative dB value represents a loss or attenuation — the output is smaller than the input. For example, −3 dB means the power ratio is approximately 0.5, meaning power is halved. Positive dB values indicate gain.

Is 20 dB twice the power ratio of 10 dB?

No — decibels are logarithmic, not linear. 10 dB corresponds to a power ratio of 10, while 20 dB corresponds to a power ratio of 100. So 20 dB is ten times the power ratio of 10 dB, not twice.

Where are dB to ratio conversions used in practice?

dB to ratio conversions are essential in audio engineering (measuring sound pressure levels), RF and antenna design (signal gain and loss), telecommunications (signal-to-noise ratio), and electronics (amplifier gain). Any field dealing with signal strength, power levels, or intensity comparisons relies on decibel calculations.

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