Sound level meter
A phone can show you useful relative sound levels — quiet room versus busy street versus power tool — but it is not a calibrated instrument, and it cannot be used for anything official.
| Sensor used | Built-in microphone |
|---|---|
| Unit | Decibel-style level (dB), uncalibrated |
| Useful range | Roughly 35–90 dB on typical hardware |
| Cannot do | Replace a Class 1 or Class 2 sound level meter, or support any workplace, legal or noise-complaint measurement |
The mechanism, not the marketing.
The microphone converts air pressure changes into a voltage. The app takes that signal, computes its root-mean-square amplitude over a short window, and converts it to a decibel-style logarithmic scale — which is why the number moves in a way that matches how loudness actually feels.
Decibels are a ratio, not an absolute quantity. A real sound level meter is calibrated against a known reference source so that its zero point means something. A phone has no such reference, so it reports a level on a scale that is consistent with itself but not anchored to anything external.
What a phone cannot do here.
- Android phones apply automatic gain control, noise suppression and echo cancellation to the microphone path. These are tuned to make voice calls sound good, and they actively work against accurate level measurement by quietly boosting soft sounds and compressing loud ones.
- Phone microphones clip. Most saturate somewhere around 90 to 100 dB SPL, so genuinely loud environments — a concert, a chainsaw, a gunshot — read far lower than they are, and the error grows exactly where accuracy would matter most for hearing safety.
- The frequency response is not flat. Phone microphones are tuned for speech, so bass is under-reported and the extremes at both ends roll off.
Is a phone decibel meter accurate?
For relative comparisons, yes — it will reliably tell you that one room is louder than another. For absolute values it is not, because the microphone is uncalibrated and the audio path applies automatic gain control.
Can I use it for workplace noise compliance?
No. Occupational noise measurement requires a Class 1 or Class 2 sound level meter meeting IEC 61672, calibrated against a reference source. No phone app qualifies, whatever it claims.
Why does the reading stop rising in very loud places?
The microphone has clipped. Once the input saturates, louder sound cannot produce a larger signal, so the number plateaus below the true level.
Every sensor your phone has, in one app.
15 tools and a multi-sensor CSV logger. Free, with a one-time remove-ads purchase.
Get Sensor Lab on Google Play