Decibel Calculator
Measure the sound level around you with your microphone, convert between decibels and power or amplitude ratios, or add up several sound sources.
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Uses your microphone to show a live level. Browsers can't read calibrated sound pressure, so readings are relative (dBFS, where 0 is the loudest the microphone can record) unless you calibrate below against a real sound level meter or a known source.
How to measure decibels
- Choose Live microphone level and click Start listening to measure the sound around you.
- Pick Slow for steady background noise or Fast for changing sounds, and add a calibration offset if you have a reference meter.
- Or choose a calculation: ratio to decibels, decibels to ratio, or combining several sound levels.
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.
The live meter works like a real sound level meter. It turns off the browser's call processing (automatic gain, noise suppression and echo cancellation), which would otherwise keep changing the level on its own. It filters out rumble below 20 Hz, and it averages the signal's energy over time. Slow (a 1-second time constant) gives a steady reading for background noise; Fast (125 ms) follows changes like speech. The figures update four times a second. Leq is the energy-average level since you started or last reset, which is the usual single number for "how loud was it here". Min and max are the quietest and loudest the weighted level has been.
Phone and laptop microphones aren't calibrated, so readings start in dBFS (decibels relative to the loudest the microphone can record, so they're negative). To read approximate dB SPL, put your device next to a real sound level meter, or next to a source of known level, and set the calibration offset until the two agree. The offset is remembered on this device. Most phone microphones lose accuracy above about 90–100 dB SPL.
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.
Questions about decibels
How accurate is a phone or laptop decibel meter?
A guide rather than a certified measurement, as microphones vary. Calibrate against a real sound level meter for better accuracy.
How loud is too loud?
Long exposure above about 85 dB, like heavy traffic, can damage hearing over time. Busy restaurants are around 70–80 dB and concerts can exceed 100 dB.
How do I add decibels together?
Not by simple addition: two 70 dB sources make about 73 dB. Use the combine option to add any number of levels.
What is the difference between 10·log and 20·log?
Use 10·log₁₀ for power ratios and 20·log₁₀ for amplitude ratios such as voltage or sound pressure, because power is proportional to amplitude squared.