On iPhone, the free NIOSH SLM app is the most rigorously validated decibel meter: built by the U.S. workplace safety institute and tested to within ±2 dBA. For more features on iPhone, such as extra weightings, frequency analysis and noise reports, Decibel X is the full-featured paid option. For an easy, free meter on both iPhone and Android with plain-English context and exposure guidance, there’s our app, Sound Meter dB. If you wear an Apple Watch, its built-in Noise app gives you passive alerts without opening anything.
No app turns a phone into a certified instrument. The differences come down to validation, features and how clearly each app tells you what the number means.
Decibel meter apps compared #
| App | Platforms | Price | Weightings | Best for |
|---|---|---|---|---|
| NIOSH SLM | iPhone, iPad (also Mac with Apple silicon and Vision Pro) | Free, no ads or in-app purchases | A, C, Z | Validated readings, workplace-style metrics |
| Decibel X | iPhone (App Store listing checked) | Free with subscriptions and add-ons | A, B, C, Z, ITU-R 468 | Power users, frequency analysis, reports |
| Apple Watch Noise | Apple Watch | Built in | Not specified by Apple | Passive alerts during the day |
| Sound Meter dB | iPhone and Android | Free with ads, no in-app purchases | A, flat (Z) | Plain-English readings, exposure time, sessions |
Prices and features were checked on the App Store and the developers’ own pages in September 2026. App pricing changes often, so confirm on the listing before you pay.
NIOSH SLM: the most validated free option on iPhone #
The NIOSH Sound Level Meter app comes from the National Institute for Occupational Safety and Health, the U.S. research agency that studies workplace hearing loss. It grew out of NIOSH’s own research on how inaccurate most sound apps were.
What it does well. It measures with A, C and Z weighting and reports LAeq, TWA, max and peak levels, plus noise dose and projected dose under NIOSH and OSHA criteria. You can calibrate the internal microphone or a calibrated external one. NIOSH says it tested the app in its acoustics lab and found it accurate within ±2 dBA, and that with a calibrated external microphone it meets Type 2 requirements of the IEC 61672-3 standard. It’s free, with no ads and no in-app purchases.
Where it falls short. It’s iOS only. NIOSH says the Android market is too fragmented across manufacturers for it to verify an Android version. The interface is built for occupational use, so casual users may find the dose and TWA numbers more than they need. More in our NIOSH SLM app guide.
Choose it if you have an iPhone and want the most defensible free readings, especially for work.
Decibel X: the most features on iPhone #
Decibel X, from SkyPaw, is a long-running sound level meter app with a deep feature list. According to its App Store listing, it offers ITU-R 468, A, B, C and Z weighting filters, a dosimeter with NIOSH and OSHA settings, calibration tools including octave and third-octave options with saved profiles, real-time FFT and bar graphs for frequency analysis, noise reports with data export, Health app integration and an Apple Watch display.
The cost. The app is free to download, but much of the depth sits behind in-app purchases. The App Store listed weekly ($1.99), monthly ($5.99) and annual ($49.99) memberships, plus one-off add-ons for extra weightings ($1.99) and data export ($2.99), at the time of writing.
Choose it if you want frequency analysis, detailed reports or specialist weightings, and don’t mind paying for them. Skip it if you only need to know how loud a room is.
Apple Watch Noise: passive alerts, no effort #
If you have an Apple Watch, you already have a noise meter. Apple says the Noise app measures ambient sound levels and the duration of exposure using the watch’s microphone, doesn’t record or save sounds to do it, and can notify you with a tap on the wrist when levels rise to a point that could affect your hearing.
What it does well. It works in the background, so you get warned at a concert or a loud workplace without thinking to check.
Where it falls short. It’s a warning system, not a measuring tool. You don’t get calibration, weighting choices or saved sessions you can export for a noise log.
Choose it if you want everyday awareness with zero effort. Pair it with a phone meter when you need a proper measurement.
Sound Meter dB: free on both platforms, with context #
Sound Meter dB is our app, so weigh this section accordingly. We’ve tried to describe it as plainly as the others.
What it does well. A live reading ten times a second on a 0 to 120 dB dial with eight color zones, and a plain-English label and comparison for each reading (“quiet library,” “vacuum cleaner,” “rock concert”). A-weighted or flat readings, Fast or Slow response, and a true Leq. A 30-second history graph with the 85 dB line, NIOSH-based safe-exposure time, and a count of time spent over 85 dB. Sessions are saved on the phone with timelines and export to CSV. Focus mode is a full-screen reading that turns red above a threshold you choose, aimed at classrooms and workshops. There’s a calibration offset for matching a reference meter, and the app is available in six languages. Audio is analyzed on the device and nothing is recorded or uploaded.
Where it falls short. No C-weighting, no dose percentage or TWA report, and no frequency analysis. It isn’t validated the way NIOSH SLM is, and it says so: readings are “good estimates for awareness and comparisons,” not a replacement for a Class 1 or Class 2 meter. It’s supported by ads, with a banner under the meter and an occasional ad when the app opens. Every feature is free.
Choose it if you want a simple, free meter on iPhone or Android that tells you what the number means and how long it’s safe.
What about Android decibel meter apps? #
Android is harder to recommend with confidence. NIOSH tested only 4 of 62 Android apps in its 2014 study, and it hasn’t released an Android version of its own app because microphones and audio processing vary so much between manufacturers. That doesn’t make every Android meter bad. It means you can’t assume one phone’s accuracy carries over to another.
When choosing an Android sound meter, look for:
- A-weighting (dBA), so readings line up with hearing limits
- Leq, not only a bouncing live number or a simple average
- A calibration offset, so you can match a reference meter if you get access to one
- Clear privacy terms. A meter should analyze sound, not record or upload it
- Honest accuracy claims. Be wary of apps that call themselves “professional” or “certified” without explaining how they were tested
Sound Meter dB covers those points on Android. Whatever you pick, calibrate it once against a known reference if you can. See how to calibrate a sound meter app.
How accurate are these apps, really? #
Even the best app depends on your phone’s microphone. NIOSH’s research found that a handful of iOS apps came within about ±2 dB of a reference meter, and that external calibrated microphones improved results to within ±1 dB. For everyday checks, a good app is plenty accurate. For compliance or legal work, you need a certified meter. See how accurate phone sound meters are and sound meter app vs SPL meter.
Frequently asked questions #
What is the most accurate decibel meter app? #
On iPhone, the free NIOSH SLM app has the strongest validation, tested by NIOSH to within ±2 dBA. No Android app has an equivalent official validation, so calibrating against a reference meter matters more on Android.
Is there a free decibel meter app without ads? #
Yes. NIOSH SLM on iPhone has no ads and no in-app purchases. Sound Meter dB is free with ads, and nothing is locked behind a purchase. Decibel X is free to download, with paid memberships and add-ons.
Can a decibel meter app be used for OSHA compliance? #
Not on its own. OSHA monitoring should use instruments that meet the relevant standards, used according to procedure. NIOSH says its app, paired with a calibrated external microphone, meets Type 2 requirements, which makes it useful for screening, but employers typically still use certified meters and dosimeters for compliance records.
Do decibel meter apps record audio? #
Some can, for features like recording clips. Sound Meter dB and Apple’s Noise app analyze sound without saving it. Check each app’s privacy policy and permissions if that matters to you.