Sound Level Converter

Enter a decibel value or a power/voltage ratio and read the conversions in the other column. The tool computes dB SPL from pressure ratios, dB from power ratios using 10·log₁₀, and dB from voltage ratios using 20·log₁₀.

Useful when reading audio spec sheets that mix conventions — amplifier output in dBV, mic sensitivity in dB SPL, headroom in dBu. Punch one in, get the others, stop second-guessing which factor of two applies.

Reference levels (0 dBV = 1 V, 0 dBu = 0.775 V, 0 dB SPL = 20 µPa) are listed next to each field so you can see the assumption baked into the conversion.

Decibels are a logarithmic ratio, but the scaling factor depends on whether the underlying quantity is a power-like or amplitude-like. Power, intensity, energy density: dB = 10 · log10(ratio). Voltage, sound pressure, current: dB = 20 · log10(ratio), because power scales with the square of these quantities, and the log of a square is twice the log. Forgetting the factor of two is the single most common dB mistake — a 6 dB voltage gain is roughly a 2× voltage ratio, not a 2× power ratio.

Worked example. A microphone has sensitivity -38 dBV/Pa. Voltage at 1 Pa SPL (94 dB SPL) is therefore 10^(-38/20) = 0.01259 V = 12.6 mV. Plug that into a preamp with 40 dB gain, and the output is 12.6 mV × 10^(40/20) = 12.6 mV × 100 = 1.26 V. Note the gain calculation uses 20·log because the gain spec is in voltage dB. If your preamp instead spec'd 40 dB power gain, the same input voltage would only multiply by 10 (the square root), giving 0.126 V output. Different specs, same number, very different results.

Reference levels matter. 0 dBV is 1 volt RMS. 0 dBu is 0.775 V RMS (a hangover from the 600-ohm telephony era — 1 mW into 600 ohms). 0 dBm is 1 milliwatt — pure power, no impedance assumption baked in. 0 dB SPL is 20 µPa, the threshold of human hearing at 1 kHz. The tool labels each unit with its reference so you don't accidentally compare a dBu spec to a dBV spec and get a 2.21 dB error nobody notices until the system is built.

A frequent acoustics mistake: doubling sound power adds 3 dB; doubling sound pressure adds 6 dB; doubling subjective loudness takes about 10 dB. Three different "doublings" depending on what you're measuring. The tool computes ratios; the perceptual side belongs in psychoacoustics references.