Decibel Shield

Can your iPhone measure decibels accurately?

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. 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. That research is the reason the free NIOSH Sound Level Meter app exists at all: 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, which is why the NIOSH app shipped on iOS only.

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:

  1. Take the case off. Thick cases partially block or redirect sound into the mic port and can shift readings by several dB.
  2. 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.
  3. 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.
  4. Expect bass to under-read. Phone mics roll off low frequencies, so a subwoofer that shakes the room registers quieter than it feels.

Try it now

You can estimate your current noise level with the free online decibel meter right in your browser, or get calibrated readings, history, and exposure alerts with Decibel Shield for iOS.

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