How phone decibel meters work, and how accurate they are

From microphone to dBA

A meter app reads the microphone as a stream of numbers between −1 and +1. It filters them with the A-weighting curve, squares and averages them over a short time (the standard “fast” and “slow” responses), and takes 10 × log₁₀ of the result. That gives a level relative to the microphone’s full scale (dBFS). To turn it into dB SPL, the app adds an offset that depends on the microphone’s sensitivity, which only calibration can tell it.

How accurate are they?

NIOSH researchers Kardous and Shaw (JASA 2014) found that of 192 apps (more than 130 iOS, 62 Android) only 10 iOS apps met their criteria and 4 Android apps were tested; just 4 iOS apps were within ±2 dB of a reference meter. Their 2016 follow-up found the same 4 apps were within ±1 dB when used with external calibrated microphones. The NIOSH Sound Level Meter app (iOS) is stated to be accurate within ±2 dBA.¹ Results depend on the phone model, the app and whether the app was calibrated for that model. Phone microphones are built for speech, so they also tend to clip or compress at very high levels.

Why browser meters are rougher

A web page cannot know which microphone it is listening to or how sensitive it is. Browsers also apply echo cancellation, noise suppression and automatic gain control for calls; a meter must ask for them to be switched off, and not every browser obeys². The live meter on this site asks for all three to be turned off, tells you if the browser refused, filters with the IEC A-weighting curve, and lets you calibrate against a real meter.

Getting a better reading

Calibrate once against a proper sound level meter or a calibrator, at a steady level.
Hold the phone away from your body, microphone pointing at the source, and keep fingers off the microphone holes.
Use a steady sound and read the slow response or the average (L_eq), not a single fast spike.
For workplace decisions use a certified class 1 or class 2 meter or a dosimeter.

Questions

Can I use my phone to measure noise at work?

As a first check, yes. For compliance or legal purposes, use a certified meter or dosimeter.

Why does my laptop read lower than my phone?

Different microphones have different sensitivities and processing. Without calibration each device needs its own offset.

Sources

NIOSH researchers Kardous and Shaw (JASA 2014) found that of 192 apps (more than 130 iOS, 62 Android) only 10 iOS apps met their criteria and 4 Android apps were tested; just 4 iOS apps were within ±2 dB of a reference meter. Their 2016 follow-up found the same 4 apps were within ±1 dB when used with external calibrated microphones. The NIOSH Sound Level Meter app (iOS) is stated to be accurate within ±2 dBA.
- Evaluation of smartphone sound measurement applications (Kardous & Shaw, J Acoust Soc Am 2014;135(4):EL186), Journal of the Acoustical Society of America (via PMC).more than 130 iOS apps were evaluated but only 10 apps met our selection criteria. Only 4 out of 62 Android apps were tested.The results showed two apps with mean differences of 0.07 dB (unweighted) and −0.52 dB (A-weighted) from the reference values. Two other apps had mean differences within ± 2 dB.Checked 2026-11-02.
- Evaluation of smartphone sound measurement applications (apps) using external microphones - A follow-up study (Kardous & Shaw, J Acoust Soc Am 2016;140(4):EL327), Journal of the Acoustical Society of America (via PMC).The initial study examined 192 apps on the iOS and Android platforms and found four iOS apps with mean differences of ±2 dB of a reference sound level measurement system.This study evaluated the same four apps using external microphones. The results showed measurements within ±1 dB of the reference.Checked 2026-11-02.
- Sound Level Meter App, NIOSH / CDC.Accurate within ± 2 dBA.Meets Type 2 requirements of IEC 61672:3 SLM standard with calibrated external microphone.Verifying the accuracy of an Android-based app is not currently possible.Checked 2026-11-02.
getUserMedia audio tracks can have echo cancellation, noise suppression and automatic gain control applied by the browser or OS. All three alter the signal, so a level meter should request echoCancellation: false, noiseSuppression: false and autoGainControl: false, then check the track's actual settings, because the browser may not honour the request.
- Media Capture and Streams (W3C Candidate Recommendation), W3C.Automatic gain control is often desirable on the input signal recorded by the microphone. There are cases where it is not needed and it is desirable to turn it off so that the audio is not altered.Noise suppression is often desirable on the input signal recorded by the microphone. There are cases where it is not needed and it is desirable to turn it off so that the audio is not altered.This is referred to as echo cancellation. There are cases where it is not needed and it is desirable to turn it off so that no audio artifacts are introduced.Checked 2026-11-02.
- MediaTrackConstraints: autoGainControl property, MDN Web Docs.If this value is a simple true or false , the user agent will attempt to obtain media with automatic gain control enabled or disabled as specified, if possible, but will not fail if this can't be done.Checked 2026-11-02.
- MediaTrackConstraints: noiseSuppression property, MDN Web Docs.Noise suppression is typically provided by microphones, although it can be provided by other input sources as well.Checked 2026-11-02.
- MediaTrackConstraints: echoCancellation property, MDN Web Docs.No audio is removed; no echo cancellation will take place.Checked 2026-11-02.

General information, not medical advice. For any concern about your hearing or a child’s, see an audiologist or doctor.