Decibel Calculator
Convert between decibels and power/amplitude ratios, or add up multiple sound sources.
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Uses your microphone to show a live relative level — browsers have no way to read calibrated sound pressure (real dB SPL), so this isn't a substitute for a real SPL meter. Useful for watching level changes, not for an absolute reading.
How these conversions work
The decibel is a logarithmic ratio, not an absolute unit — it always compares two quantities. For power-like quantities (acoustic power, electrical power, sound intensity), dB = 10·log₁₀(P2/P1). For amplitude-like quantities (voltage, sound pressure, pressure amplitude), dB = 20·log₁₀(A2/A1) — the factor of 20 instead of 10 accounts for power being proportional to amplitude squared.
Combining sound sources isn't simple addition because decibels are logarithmic: two equally loud 70 dB sources together produce about 73 dB, not 140 dB. This tool converts each level back to linear intensity, sums them, and converts the total back to dB using L = 10·log₁₀(Σ 10^(Li/10)). Nothing entered here is sent to a server — the calculation runs as JavaScript in your browser tab.