How to use the Decibel Meter
- Click Allow microphone and start, and place the phone or laptop where you want to measure without covering the microphone.
- Measure for 30–60 seconds and watch the live reading, maximum and Leq.
- If you have a calibrated sound level meter, measure together and adjust the calibration offset until they match (saved on this device).
- Copy the result or take a screenshot and compare with the decibel reference below.
How a web decibel meter works, and its error
The tool reads the microphone signal, computes the RMS level in dBFS, weights the spectrum with the IEC 61672 A-weighting curve and adds a calibration offset to estimate dB(A). Browsers cannot know the microphone sensitivity and automatic gain may change the signal, so uncalibrated readings are only good for relative comparisons (window open vs closed, day vs night), not for enforcement or occupational health measurements.
Typical sound levels
About 20–30 dB: a quiet bedroom at night. About 40 dB: a library. About 50–60 dB: a quiet office or normal conversation. About 70 dB: busy traffic. About 85 dB: a noisy factory or power tools. Over 100 dB: concerts. NIOSH recommends no more than 85 dB(A) over 8 hours, OSHA’s legal limit is 90 dB(A), and WHO recommends bedroom night noise below 30 dB(A).
Leq, maximum and A-weighting
Leq (equivalent continuous sound level) is the energy average over a period and represents exposure better than instant readings. A-weighting mimics the ear’s lower sensitivity to bass and is used by most environmental noise standards; unweighted dB(Z) shows more low-frequency rumble.
Frequently asked questions
How accurate is a phone decibel meter?
Use it as a reference. Phone microphones are tuned for speech and the browser does not know their sensitivity. After calibrating against a professional meter, it compares relative changes well on the same device and setup.
Why does it read 30–40 dB in a silent room?
That is the noise floor of the microphone and room plus the default calibration offset. In very quiet rooms the phone microphone’s own noise can exceed the real ambient level, so readings below about 30 dB are usually unreliable.
Can I use it as evidence for a noise complaint?
Not as formal evidence. It helps log when noise happens and how loud it is relatively. For official complaints or legal action, contact your local authority or an accredited lab with a verified sound level meter.
What is the calibration offset?
It is a value added to dBFS. Measure alongside a calibrated meter or a source of known level and adjust the offset until both match; the setting is saved in this browser.
Does the page need to stay open?
Yes. Some browsers pause the microphone or slow processing in the background, so keep the page in front and avoid locking the screen.