Decibel Meter

How to use the decibel meter

1. Press Start measuring and allow the microphone when your browser asks.
2. Watch the big number: it is the current level. Choose Fast (125 ms) to follow quick changes or Slow (1 s) for a calmer reading in the Response list.
3. The Min, Average (Leq) and Max values and the Duration build up while you measure. The graph shows the last 60 seconds.
4. Press Reset statistics to start a fresh measurement, and Stop to turn the microphone off. The statistics stay on screen after stopping.
5. Optional: enter a Calibration offset (dB) to turn the raw values into rough sound-pressure estimates (see below).

Everything is computed in your browser. The sound is analysed in memory and never recorded or uploaded.

Important: these are relative estimates, not calibrated measurements

A phone, laptop or headset microphone is not a sound level meter. By default, this tool shows dBFS: decibels relative to the loudest signal the microphone input can digitize (0 dBFS). Values are negative, and what they mean in real sound pressure depends on the microphone’s sensitivity, its frequency response, the gain set by your operating system, and any processing the device applies that the browser can’t disable. Two phones in the same room can differ by 10 dB or more.

This tool also doesn’t apply A-weighting (the dB(A) curve used in regulations) and isn’t tested against the IEC 61672 standard. Use it to compare levels over time or between places with the same device (“the fan is 6 dB quieter on setting 2”), not to prove compliance with noise limits or to assess the risk to your hearing. For those, use a certified sound level meter.

Calibration offset

If you have access to a real sound level meter, you can make this tool’s readings roughly match it:

1. Place your device next to the reference meter and play a steady sound, such as pink noise or a fan.
2. Type the reference meter’s reading in Reference reading (dB).
3. Press Match reference. The offset is computed as reference − current dBFS and filled in for you.

You can also type an offset directly. Every value, including the graph, is shifted by the offset, and the unit changes from dBFS to dB (est.). The offset is only valid for that device, microphone and browser, and only roughly for other sounds: a phone mic may under-read low rumble and over-read hiss compared with the meter.

How the numbers are calculated

The level of each block of about 43 ms of audio is 10 × log10 of the mean squared sample value; a full-scale sine wave reads about −3 dBFS. Like a traditional meter, the display is smoothed with an exponential time constant of 125 ms (Fast) or 1 s (Slow). Average (Leq) is the energy-equivalent level: the power is averaged over time and then converted to decibels, so a loud minute counts much more than a quiet one, which is how noise exposure is usually summarized. The first half second after starting is ignored because microphones often pop when they turn on.

Decibels are logarithmic: +3 dB is double the sound power, +10 dB is perceived as roughly twice as loud.