# 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 > Canonical page: https://elysiatools.com/en/tools/decibel-calculator - **Category:** Math & Numbers - **Keywords:** decibel, dB, power ratio, voltage ratio, amplitude ratio, dBm, dBW, dBV, dBu, dBFS, SIL, 10 log, 20 log, audio, RF, acoustics ## Overview 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. ## Inputs - **Mode** (select) - **Quantity Type** (select) - **Measured Value** (number): e.g. 100 (power/amplitude value) - **Reference Value** (number): e.g. 1 (the baseline P₀ or V₀) - **Decibels (dB)** (number): enter dB when converting dB → ratio - **Absolute Unit** (select) - **Absolute Value** (number): physical value (W, V, FS, or W/m²) ## When to use - When calculating signal gain or attenuation in RF, audio, or telecommunications systems using power or voltage ratios. - When converting absolute physical measurements like watts or volts into standard logarithmic units like dBm, dBu, or dBV. - When translating decibel values back into linear ratios to determine exact amplification or attenuation factors. ## How it works - Select the calculation mode: convert a ratio to decibels, convert decibels back to a ratio, or calculate absolute levels. - Choose the quantity type (Power Ratio using 10·log or Amplitude/Voltage Ratio using 20·log) and define your measured and reference values. - For absolute levels, select the target unit (such as dBm, dBu, or dBV) and input the physical value to compute the corresponding decibel level. ## Use cases - Audio engineering calibration to match line-level signals between dBu and dBV equipment. - RF link budget analysis to convert transmitter output power from watts to dBW or dBm. - Acoustic analysis to determine Sound Intensity Level (SIL) from measured physical power density. ## Frequently asked questions ### 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? 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