HowLoudCan I Use My Phone as a Decibel Meter?
Yes. A modern phone with a decent meter app or a browser-based meter reads within about ±3 to 5 dB of a professional sound level meter between roughly 40 and 95 dB(A). That is accurate enough to compare rooms and appliances, check headphone or classroom levels, and document a noise problem. It is not accurate enough for legal evidence or workplace compliance.
What the research says
NIOSH tested smartphone sound-meter apps against a Type 1 reference meter in a controlled chamber. The best iPhone apps were within ±2 dB(A) of the reference across 65–95 dB; the spread on Android was wider because of the variety of microphones and audio pipelines, from ±3 dB on some devices to more than ±10 dB on others. With an external calibrated microphone, iPhone apps met Type 2 tolerances. The lesson: the app matters less than the microphone and whether the system's automatic gain control is defeated.
How to measure with a phone
- Use a meter that turns off noise suppression and automatic gain. The HowLoud online meter and the HowLoud app request raw audio from the microphone.
- Hold the phone at arm's length, screen facing you, bottom microphone toward the sound, about 1–1.5 m above the floor. Do not cover the microphone with your hand, and take it out of a thick case.
- Stand still and stay quiet. Your own breathing and clothes rustling read 40–50 dB at that distance.
- Measure for at least 30 seconds and read the average (Leq), not the moment-to-moment value. Note the peak separately.
- Repeat at the same spot at different times if you are documenting a recurring problem.
Calibrating your phone
Every microphone has its own sensitivity, and the meter converts the digital signal (dBFS) into a dB SPL estimate with a fixed offset. If you have access to a real sound level meter, even a cheap one, run both side by side on a steady sound such as a fan and adjust the calibration slider until they match. Without a reference, two sanity checks help: a quiet room at night should read about 30–35 dB, and normal conversation at arm's length about 60–65 dB.
Where phones fall short
- Very quiet sounds. The microphone's own electronic noise sets a floor around 30 dB, so a 20 dB room reads 30.
- Very loud sounds. Above roughly 100–110 dB the microphone or the analogue stage clips and the reading stops rising. Gunshots, fireworks and concert speaker stacks are out of range.
- Peak measurements. Phones sample the level many times a second but cannot capture the true instantaneous peak of an impulse the way a Class 1 meter does.
- Frequency response. Phone microphones are tuned for voice; readings of deep bass or high hiss are less reliable, which matters for dBC and dBZ measurements.
- Legal standing. No phone app is certified to IEC 61672. A council officer or court needs a Class 2 or Class 1 instrument with a calibration certificate.
iPhone vs Android
iPhones have a small number of microphone models and a consistent audio pipeline, so calibration offsets carry over well between apps and devices. Android covers thousands of devices; readings on flagship phones are usually fine, while budget phones may need a calibration offset of 10 dB or more. On either platform, a Bluetooth headset microphone should never be used for measurements.
Frequently asked questions
Is there a built-in decibel meter on iPhone?
Not for ambient sound. iOS shows headphone audio levels in Settings › Hearing and the Apple Watch has a Noise app; measuring the room needs an app or a web meter.
Does an online decibel meter work as well as an app?
For live readings, yes: both use the same microphone and the browser can request raw audio. Apps add saved history, background measurement and exports.
Why does my phone read lower than a real meter?
Usually automatic gain control or noise suppression in the operating system, or a case covering the microphone. Use a meter that disables processing and calibrate against the reference.