The NIOSH Sound Level Meter App: How to Measure Workplace Noise and Read the Results

The free NIOSH Sound Level Meter (SLM) app turns an iPhone into a rough sound meter. Open it in your work area, let the dBA reading settle for a minute or two, and note the average. Readings at or above 85 dBA over a full shift signal a real hearing risk, and that is your cue to add protection and book a hearing check.

Why measuring noise matters

You cannot judge dangerous noise by ear alone. Loud sound damages the tiny hair cells in the cochlea, and once those cells die, they do not regenerate — the hearing loss is permanent (NIDCD). NIOSH sets the recommended exposure limit at 85 dBA averaged over an 8-hour shift (CDC/NIOSH). Above that, risk rises quickly, because every 3 dB increase roughly halves the safe exposure time.

The problem is that most people underestimate how loud their workplace is. A number on a screen removes the guesswork. That is the whole point of measuring: turning a vague "it seems loud" into a figure you can act on. For the full picture on shift limits and control methods, read our pillar guide, Is Your Job Damaging Your Hearing? Safe Noise Levels at Work (NIOSH Guide).

How the NIOSH Sound Level Meter app works

NIOSH built and tested the app with acoustics engineers so an ordinary iPhone can give a reasonably accurate reading (CDC/NIOSH). It is currently available for iOS only. To use it:

1. Download "NIOSH SLM" from the App Store and open it in your actual work area, during normal operations. 2. Hold the phone at arm's length, near ear height, with nothing covering the microphone. 3. Watch the large central number — this is the instantaneous dBA level. It will jump around with each sound. 4. Let it run for a minute or more, then read the LAeq (average) and TWA (time-weighted average) fields, which smooth out the spikes.

A note on accuracy: the built-in iPhone microphone is not laboratory-calibrated, so treat the app as a screening estimate. It is excellent for flagging risk. It is not a substitute for a calibrated meter in a formal OSHA noise survey (OSHA).

What the readings mean

Use dBA bands as a practical guide (CDC/NIOSH, ASHA):

• Below 70 dBA — safe. Normal conversation sits around 60 dBA and poses no risk over time.
• 70 to 84 dBA — generally low risk, but stay aware if exposure is all day, every day.
• 85 dBA and above — the action zone. At this level over an 8-hour shift, protection is recommended (CDC/NIOSH).
• 100 dBA and above — high risk. Safe exposure is around 15 minutes without protection, and less as levels climb higher.
• 120 dBA and above — sound can cause immediate harm and pain.

A simple field test backs up the meter: if you have to raise your voice to talk to someone an arm's length away, the noise is likely near or above 85 dBA.

When to add hearing protection

If your average reading reaches 85 dBA or higher, act. The two proven steps are reducing the noise at its source and wearing hearing protectors — foam earplugs, earmuffs, or both together for very loud settings (NIDCD). Where possible, engineering and administrative controls, such as quieter equipment or rotating staff out of noisy zones, come before relying on protectors alone (CDC/NIOSH).

Protectors only work when worn correctly and consistently. A well-fitted foam plug can cut exposure by 20 to 30 dB; a plug worn loosely may cut far less.

What to do after a loud reading

A high reading is a signal, not a diagnosis. Early noise-induced damage often shows up first in the high frequencies and can go unnoticed for years. The only way to know your current hearing status is a professional test.

If you work in or around noise, book a baseline hearing test and repeat it yearly to track any change over time. Our audiologists can also advise on properly fitted protection for your specific workplace — contact us to arrange a visit, and a home visit is available if getting to the clinic is difficult.

Urgent note: if you notice a sudden drop in hearing, or ringing (tinnitus) that does not settle after a loud exposure, treat it as urgent and see an audiologist or doctor within a day or two, as prompt care can matter.