A noise dosimeter is a small meter worn by a person, usually clipped at the shoulder, that logs noise for a whole shift and reports a dose: the percentage of the day’s allowed exposure used up. A sound level meter is handheld or tripod-mounted and measures the noise at one spot, over a short period. Dosimeters answer “how much noise did this worker get today?” Sound level meters answer “how loud is it here, and what’s causing it?”
Most workplace noise programs use both. The meter finds the loud areas and sources, and the dosimeters measure what people actually receive as they move around.
Dosimeter vs sound level meter at a glance #
| Noise dosimeter | Sound level meter | |
|---|---|---|
| Worn or held | Worn by the worker, microphone near the ear | Held or mounted by the person measuring |
| Measures | Personal exposure as the worker moves | Level at one location |
| Typical duration | Full shift | Seconds to hours |
| Main outputs | Dose (%), TWA, projected dose, Leq, max, peak | Leq, max, peak, live level; often frequency analysis |
| Best for | Compliance with personal exposure limits, mobile jobs | Area surveys, finding sources, noise control, checking a machine |
| Weakness | Doesn’t tell you which source caused the noise | Can miss what a mobile worker actually receives |
What does a noise dosimeter measure? #
A dosimeter integrates noise over time and compares it with an exposure criterion. Under OSHA’s noise standard, dose is calculated as:
D = 100 × (C1/T1 + C2/T2 + … + Cn/Tn)
C is the time spent at a given level and T is the time allowed at that level. A dose of 100% equals the permissible exposure limit. OSHA converts dose to an 8-hour time-weighted average with TWA = 16.61 × log10(D/100) + 90, and requires all sound levels from 80 to 130 dB to be included in the measurement.
Dosimeters let you set the criterion level, exchange rate and threshold. That’s how the same instrument can report against OSHA (90 dBA criterion, 5 dB exchange rate) or NIOSH (85 dBA, 3 dB). The same shift can come out well under 100% by OSHA’s math and over 100% by NIOSH’s. See NIOSH vs OSHA noise limits.
Most dosimeters also report projected dose, what the dose would be if the noise continued for a full shift. That lets you run a shorter sample and still estimate the day.
What does a sound level meter measure? #
A sound level meter reports the level at its microphone, with a chosen frequency weighting (A, C or Z) and time weighting (Fast or Slow). An integrating meter also calculates Leq over the measuring period, along with max and peak. Many add octave or third-octave band analysis, which shows which frequencies dominate.
That makes a sound level meter the tool for:
- Mapping noise across a workshop or plant floor
- Finding which machine is the problem
- Checking whether a new enclosure or silencer worked
- Choosing hearing protection for specific frequencies
- Environmental and neighbor noise measurements
Which one does a workplace noise survey need? #
OSHA requires employers to develop and implement a monitoring program when information indicates that any employee’s exposure may equal or exceed an 8-hour TWA of 85 dBA. The standard allows area monitoring or personal sampling. In practice:
- Workers stay in one place with steady noise (a machine operator at a fixed station): area measurements with a sound level meter can represent their exposure.
- Workers move around, or noise varies a lot (maintenance, construction, warehouse): personal dosimetry is the reliable way to capture what they get.
- Planning noise control: a sound level meter, ideally with frequency analysis, to find and fix sources.
Many programs start with a sound level meter survey to find the loud areas, then put dosimeters on the workers who spend time in them.
Can a phone app act as a dosimeter? #
Partly. NIOSH’s free SLM app for iPhone reports noise dose and projected dose under NIOSH and OSHA criteria, and NIOSH says it meets Type 2 requirements when used with a calibrated external microphone. It’s a good screening tool. A phone in a pocket isn’t a dosimeter, though: the microphone is covered and far from the ear. Formal compliance records generally come from purpose-built dosimeters.
Sound Meter dB takes a simpler approach aimed at personal awareness. It doesn’t calculate dose percentages. Instead it shows how long the current level is safe under the NIOSH guideline and counts the total time you’ve spent over 85 dB in a session. Saved sessions keep a per-second timeline you can export as CSV. That’s useful for a worker or hobbyist who wants a quick check of a loud task, and it’s no replacement for a dosimeter when compliance is on the line. See how accurate phone sound meters are.
How do you get good dosimeter readings? #
- Calibrate the dosimeter with an acoustic calibrator before and after the shift.
- Mount the microphone on the shoulder, close to the ear that’s exposed to the most noise, and keep it clear of collars and hoods.
- Brief the worker. Tapping, shouting into the mic or covering it skews the results.
- Record the day’s tasks so you can match high readings to activities.
- Use the right settings: criterion level, exchange rate and threshold to match the standard you’re reporting against.
Frequently asked questions #
What does 100% noise dose mean? #
A 100% dose means the worker received the maximum allowed exposure for the day under the criteria the dosimeter was set to. Under OSHA’s settings, that’s the same as an 8-hour TWA of 90 dBA. Under NIOSH’s settings, it’s 85 dBA.
Can a sound level meter measure noise dose? #
Some integrating sound level meters can calculate dose, but they only measure at their own location. If the worker moves around, the meter’s dose may not match what the worker received. That’s why personal dosimeters exist.
Where is a noise dosimeter worn? #
Usually on the shoulder, with the microphone as close to the ear as practical, on the side facing the main noise source.
Is a noise dosimeter the same as a sound level meter? #
No. They use similar measuring principles, but a dosimeter is built to be worn and to report personal exposure over a shift, while a sound level meter is built to measure the level at a location. Many noise programs use both.