DecibelwerkQuick answer: iPhones don’t come with a decibel meter, but the hardware is good enough to measure sound with an app. The free options are the Noise app on an Apple Watch and NIOSH’s free Sound Level Meter app. For a reliable reading, use A-weighting, take the case off, keep the bottom microphone uncovered, hold the phone where your ears are and read the average (Leq) over at least 30 seconds.
What your iPhone can already do
There’s no sound meter in iOS. Two built-in features come close:
- Apple Watch Noise app. If you have an Apple Watch, it measures the A-weighted level around you and shows it as OK or Loud. It averages over 3 minutes and can notify you when that average passes a threshold you set (in the Watch app on iPhone, under Noise). It doesn’t record audio. Readings pause in Water Lock and while the watch’s mic or speaker is busy.
- Headphone level in Control Center. Add the Hearing control to Control Center, and it shows how loud the audio in your headphones is. It only covers what’s playing through headphones, not the room.
The free iPhone option: NIOSH Sound Level Meter
NIOSH, the US research agency for workplace safety, publishes a free meter app with EA LAB. It has no ads or in-app purchases, and it measures A, C and Z weighting, LAeq, the time-weighted average and the noise dose under NIOSH and OSHA rules. The developer reports ±2 dBA accuracy in NIOSH’s lab with the built-in microphone, and Type 2 performance with an external calibrated microphone. If you need an occupational noise dose for work, it’s the one to use.
How to get a reading you can trust
Whatever app you use, the technique matters more than the app:
- Take the case off. Many cases partly cover the bottom microphone.
- Uncover the bottom edge. Don’t hold the phone by its base, and keep fingers off the grille.
- Use A-weighting (dBA) for anything about hearing, neighbours or workplaces. Limits are written in dBA.
- Hold the phone where your ears are, pointed at the room, not pressed against the source. For a neighbour’s noise, put it where you sleep.
- Keep it still for at least 30 seconds and read the average (Leq) as well as the maximum. Single peaks mislead.
- Avoid wind and handling noise. A breeze across the microphone reads as loud low-frequency noise.
Why phone meters can disagree
| Cause | Effect | What to do |
|---|---|---|
| Automatic gain control | Quiet sounds read too loud, loud ones too quiet | Use an app that uses iOS measurement mode |
| Very quiet rooms | The microphone’s own noise shows up | Treat readings under about 35 dB as “very quiet” |
| Very loud sources | Peaks may compress above about 110 dB | Step back and measure where you’d actually stand |
| Different models | Microphones vary slightly | Calibrate against a known meter if it matters |
Calibrating means comparing with a reference: put the phone next to a calibrated meter, play a steady sound (the online tone generator works), and adjust until they agree. Decibelwerk Pro has a CAL knob for this, in half-decibel steps.
Which should you use?
| You want | Use |
|---|---|
| A warning when it gets loud, all day | Apple Watch Noise app |
| A free workplace noise dose | NIOSH Sound Level Meter |
| A clear meter, noise logs and a PDF report | Decibelwerk |
Once you have a number, see what it means in how many decibels is too loud.