Decibel Shield
Can your iPhone measure decibels? How to use it as a decibel meter
Yes, within limits. NIOSH researchers found that the best iOS sound meter apps read within about ±2 dB of professional reference meters in lab tests — good enough for awareness and exposure screening. Phone microphones still struggle with very loud peaks and are not a legal substitute for a calibrated SPL meter.
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What the research actually says
The most-cited evidence comes from NIOSH researchers Chucri Kardous and Peter Shaw, who tested smartphone sound measurement apps against calibrated laboratory reference systems (Kardous & Shaw, JASA 2014). Their findings: a handful of well-built iOS apps measured within roughly ±2 dB(A) of the reference — comparable to the tolerance of a Type 2 field meter — and accuracy improved to about ±1 dB when an external calibrated microphone was used (follow-up study, JASA 2016). The takeaway: iPhones have consistent enough audio hardware that a carefully calibrated app can do real screening work.
Why iPhones do better than Android here
Apple ships a small number of hardware models with tightly controlled microphone components, so an app can ship per-model calibration profiles. Android spans thousands of devices with wildly different microphones: in the same NIOSH study, only 4 of 62 Android apps could be tested, against 10 of more than 130 iOS apps.
Is there an app to measure sound level on an iPhone?
Yes. A sound meter app uses the iPhone’s own microphone to measure the sound level around you in decibels, and the better ones are accurate enough for everyday screening. They vary a lot, though: of the more than 130 iOS apps the NIOSH researchers looked at, only 10 met their basic criteria for testing, and 4 read within about 2 dB of the reference meter. So check what an app actually does before you trust its number.
Can you measure decibels on an iPhone for free?
Yes, two ways, and neither needs a paid upgrade for a basic reading:
- In Safari, with nothing to install. The free online decibel meter runs in the iPhone’s browser: press Start, allow the microphone, and it reads the level around you, with the minimum, average and maximum of the session and the NIOSH safe time for that level. Nothing is recorded or uploaded.
- As a free decibel meter app for iPhone. Decibel Shield, a sound meter app for iOS, is free to download from the App Store and measures without paying. An optional Premium subscription adds extras such as calibration fine-tuning; see what the app does.
Either one turns the iPhone into a decibel reader, and the same limits apply to both, because both listen through the phone’s own microphone (see where phones still fall short, below).
What should a sound meter app for iPhone do?
- State its accuracy honestly. A good app says how far off it can be and does not claim to replace a certified meter.
- Correct for your iPhone model, and let you adjust. Models differ, so a good app ships a correction for each one and lets you nudge the reading to match a reference meter you trust.
- Show averages, not just a jumping number. Hearing limits are set on average exposure over time, so look for the minimum, average and maximum of each session, not only the live figure.
- Offer A-weighting. Workplace and hearing limits are given in A-weighted decibels, which follow how loud a sound seems to the ear. See what dB(A) means.
- Put the number in context. A reading means little on its own; the useful apps tell you how long that level is safe, against the NIOSH limit of 85 dB(A) averaged over 8 hours.
- Keep a history you can export. To document a neighbour or workplace problem you need dated readings you can save, ideally as a CSV file. See measuring noise for a complaint.
- Work with an external microphone. That is where the ±1 dB result came from. See external microphones for phone measurements.
How can I measure decibels on my iPhone with Decibel Shield?
Two ways, depending on whether you want a quick reading or a running record:
| Free online meter | Decibel Shield app for iPhone | |
|---|---|---|
| Install | Nothing: runs in Safari | Free from the App Store |
| Each session | Minimum, average and maximum, with the NIOSH safe time for the level you hear | Live reading with dominant frequency, saved with date and time |
| Weighting and calibration | Approximate A-weighting switch; per-device defaults you can nudge by 1 dB | Built-in correction for each iPhone model; fine-tuning slider in Premium |
| Over time | One session at a time | Keeps measuring in the background; history and trends over weeks and months |
| Alerts | No | Notifies you when noise crosses a level you set |
| Saving | Report as CSV or PDF | History export as CSV |
| Privacy | Nothing is recorded or uploaded | Measurement runs on the phone |
Start with the free online decibel meter for a reading right now, or see what the Decibel Shield app does if you want your exposure tracked day to day.
Where phones still fall short
Phone microphones are built for voice. They roll off very low frequencies, and at high levels — sustained sound above roughly 100 dB — they can compress or clip, under-reading the true level. Wind, cases, and where you hold the phone all add error. For anything legal, occupational, or contractual, you need a calibrated meter that meets IEC 61672 — see how phone apps compare to dedicated SPL meters.
How do I get the most accurate reading from my iPhone?
Four practical habits close most of the gap:
- Take the case off. Thick cases partially block or redirect sound into the mic port and can shift readings by several dB.
- Point the microphone at the source. On most iPhones the primary mic is on the bottom edge — aim it at the noise rather than laying the phone flat on a table.
- Know the loud-end limit. Tiny phone MEMS microphones compress and clip on very loud sources — roughly the 90–100+ dB region — so concerts and machinery read lower than reality.
- Expect bass to under-read. Phone mics roll off low frequencies, so a subwoofer that shakes the room registers quieter than it feels.
