What is the difference between power and amplitude quantity types?

Power quantities use a 10·log10 multiplier (e.g., watts), while amplitude quantities use a 20·log10 multiplier (e.g., volts) because power is proportional to the square of amplitude.

What reference value is used for dBm?

The reference value for dBm is 1 milliwatt (0.001 W), representing absolute power level.

How does dBu differ from dBV?

dBu is referenced to 0.7746 volts (the voltage that delivers 1 mW into a 600-ohm load), whereas dBV is referenced to exactly 1 volt.

What does dBFS stand for?

dBFS stands for Decibels relative to Full Scale, commonly used in digital audio systems where 0 dBFS represents the maximum possible digital signal level.

Can I calculate acoustic sound intensity levels with this tool?

Yes, by selecting the SIL unit, which uses the standard acoustic reference threshold of 10⁻¹² W/m².

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Decibel Calculator (Power Ratio, Voltage Ratio, dBm/dBu/dBV)

Convert between ratios and decibels (10·log power, 20·log amplitude), and across absolute units dBm/dBW/dBV/dBu/dBFS/SIL

Details

What this tool helps you do

The decibel (dB) is a logarithmic unit for ratios.

Power quantities: dB = 10 · log₁₀(P / P₀)
Amplitude quantities: dB = 20 · log₁₀(V / V₀)

Modes: ratio↔dB conversion, and absolute levels dBm (1 mW), dBW (1 W), dBV (1 V), dBu (0.7746 V), dBFS (full scale), SIL (10⁻¹² W/m²).

Reference: 0 dB = 1×, +3 dB ≈ 2× power, +6 dB ≈ 2× voltage, +10 dB = 10× power.

Execution

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2 examples

100 W vs 1 W → 20 dB power gain

dB = 10·log₁₀(100/1) = 20 dB.

1 mW → 0 dBm (the reference)

0 dBm is defined as 1 milliwatt.

Inputs

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7 options

SettingsAdjust formats, ranges, numbers, and modes.7

ModeselectOptionalQuantity TypeselectOptionalMeasured ValuenumberOptionalReference ValuenumberOptionalDecibels (dB)numberOptionalAbsolute UnitselectOptionalAbsolute ValuenumberOptional

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Samples

Decibel Calculator (Power Ratio, Voltage Ratio, dBm/dBu/dBV)

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Examples

1. Calculating RF Amplifier Power Gain

2. Converting Audio Line Level to dBV

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