Why the Platform Matters First

Before you look at features, check your phone. On iPhone, the free NIOSH Sound Level Meter has been tested in a special sound chamber. It stays within about 2 dBA of a real meter. On Android, no app has the same proof. The CDC says it cannot check Android apps because Android phones use many different parts from many makers.

So the same app can be close to a real tool on one phone and just a rough guess on another. That is why this guide ranks apps by trust level, not by stars.

The Trust Levels, Explained Simply

• Lab-tested: A real lab checked the app against a correct meter.
• Peer-reviewed: A study checked it, and other experts can review the method.
• Vendor-claimed: The maker says it is accurate. No one else checked.
• Unverified: No accuracy number exists at all.

This difference matters. A maker's claim and a lab test are not the same thing.

How Accurate Are These Apps, Really?

Two studies sit behind most accuracy claims. Kardous and Shaw (2016) tested iOS apps with external mics. They found accuracy improved to about ±1 dB with a calibrated mic. Celestina, Hrovat and Kardous (2018) tested apps against international meter standards. The NIOSH app cites this study for its accuracy claim.

One big limit: most phone mics are built for voices, not loud rooms. Automatic gain control also flattens loud sounds. On older phones, readings stopped working correctly between about 82 and 94 dB. That range is close to where hearing damage starts. So the tool can read low and call it safe when it is not.

Best Picks by Situation

Best on iPhone: NIOSH Sound Level Meter. Free, no ads, no in-app buys. Lab-tested at ±2 dBA. It shows LAeq, time-weighted average, dose, and A/C/Z weighting. It only works on iOS. Its Type 2 claim needs an external mic.

Best for audio pros: SPLnFFT. About $3.99. Peer-reviewed. Adds L10, L95, dosimeter mode, and a spectrum analyzer. iOS only.

Best cross-platform: Decibel X. Works on iOS and Android. Free to download, but weightings and export cost about $2 to $3 each. Accuracy is vendor-claimed only.

Best free on Android: Sound Meter by rootApps. About 10 million installs. Ad-supported. No published accuracy figure. Check the package name, since many apps share this title.

Best for quiet restaurants: SoundPrint. Not a meter. It is a database of over 100,000 venues rated by noise.

Best for classrooms: Too Noisy and ClassDojo Noise Meter. These are behavior tools, not meters.

How Loud Is Too Loud?

NIOSH says 85 dBA for eight hours is the safe limit. Every 3 dB above that halves the safe time. At 100 dBA, that is about 15 minutes. OSHA uses a looser rule: 90 dBA with a 5 dB exchange rate. OSHA's rule is the only one enforced by law.

LevelNIOSH Safe TimeExample85 dBA8 hoursHeavy traffic91 dBA2 hoursLawn mower100 dBA15 minutesChainsaw112 dBA~1 minuteRock concert

If you also work with creative tools and want to see how they compare, this guide to the best AI video generators is a useful read.

Simple Steps for a Better Reading

1. Take off your phone case.
2. Hold the phone at arm's length.
3. Avoid wind and handling noise.
4. Measure for several minutes, not seconds.
5. Reset between readings.

To calibrate, go to a very quiet room and set the offset until the app reads about 20 to 30 dB. A silent room is not 0 dB. Check your app's privacy label too. The NIOSH app collects no data.

When an App Is Not Enough

No app is legal evidence or an OSHA record. An app is like a smoke alarm. It tells you to act. It does not prove a case. For a real complaint, buy a calibrated Type 2 meter, which starts around $50 to the low hundreds. Use an app to decide if a space needs a real test. Do not use it as the test.

Final Word

On iPhone, start with the free NIOSH app. It is the only one with a real lab test. Add SPLnFFT if you need pro tools. On Android, use Sound Meter by rootApps and treat every reading as a comparison, not a fact. For legal or work records, buy a real meter.