You can test sound decibels with a handheld sound level meter, a wearable noise dosimeter, or a smartphone app. The method you choose depends on whether you need a quick spot check, a full-day exposure reading, or just a rough estimate. Each approach has tradeoffs in accuracy, cost, and convenience, and getting reliable numbers requires more than just pointing a device at a noise source.
Sound Level Meters vs. Dosimeters vs. Apps
A sound level meter (SLM) is the standard tool for measuring decibels at a specific location and time. You hold it or mount it on a tripod, aim the microphone at the sound source, and read the level on the display. This works well for checking whether a piece of equipment, a venue, or a room meets a noise threshold.
A noise dosimeter is a small device you clip to your shoulder or collar, and it records your cumulative noise exposure over hours. It’s designed for workers who move through different noise environments throughout a shift. Research from the Mine Safety and Health Administration found no practical difference between dosimeter and SLM readings in steady noise, but in rapidly changing sound environments, dosimeters tend to capture short bursts of loud noise more accurately. If you need to know your total daily exposure rather than the level at one moment, a dosimeter is the better choice.
Smartphone apps are the most accessible option but the least reliable. A NIOSH study tested 10 iOS apps against a calibrated reference meter and found that only three measured within plus or minus 2 decibels of the true level. Android apps performed even worse: out of 62 examined, only four partially met the study’s selection criteria for testing. Phone apps can give you a general sense of whether a space is loud, but they shouldn’t be trusted for compliance checks or hearing protection decisions.
How to Position the Microphone
Where you place your meter matters as much as the meter itself. Point the microphone directly at the sound source, and keep it at ear height, roughly 4 to 5 feet above the ground for a standing adult. This simulates what a person’s ears would actually receive.
Clear away anything between the microphone and the source. Furniture, partitions, and walls reflect or block sound waves, which can push your reading higher or lower than the true level. If you’re measuring outdoors, stay away from building facades and fences for the same reason. Mounting the meter on a tripod helps keep it steady and prevents your own body from acting as a reflector.
Choosing the Right Weighting
Sound level meters let you apply frequency weightings that filter the measurement in different ways. The two you’ll encounter most often are A-weighting and C-weighting.
- A-weighting (dBA) filters the sound to match how human ears perceive noise. It reduces the contribution of very low and very high frequencies, since our hearing is less sensitive to those. Nearly all workplace noise regulations and environmental standards use dBA.
- C-weighting (dBC) applies a much flatter filter and is used for measuring peak sound levels, especially sudden loud events. Workplace guidelines from the WHO, for example, set the peak limit at 135 dBC.
- Z-weighting applies no filter at all. It captures the raw sound pressure across all frequencies and is mainly useful for analyzing the sound source itself, like testing a speaker’s frequency response in manufacturing.
For most general purposes, including checking workplace noise, traffic, music venues, or home appliances, A-weighting is the correct setting.
Accounting for Background Noise
If you’re trying to measure one specific sound source, background noise can contaminate your reading. Because decibels work on a logarithmic scale, you can’t simply subtract one number from another the way you would with regular arithmetic.
The general rule: your source needs to be at least 10 decibels louder than the background for your measurement to reliably represent the source alone. If the gap is smaller than that, the background is inflating your reading in a way that’s hard to correct. Before measuring your target sound, take a reading of just the background with the source turned off. If the difference between the two readings is less than 3 dB, the measurement is essentially unusable for isolating the source. Between 3 and 10 dB, correction charts exist that tell you how many decibels to subtract, but accuracy drops the closer those two numbers get.
Calibrating Your Meter
Professional sound level meters need calibration before each use. An acoustic calibrator is a small device that fits over the microphone and emits a known tone, typically 114 dB at 1,000 Hz. You insert the microphone into the calibrator cavity, power it on, wait about 10 seconds for the output to stabilize, then adjust the meter until its display matches the calibrator’s reference level. The ambient noise around you should be below 88 dBA while calibrating, or the reference tone can be drowned out.
If you skip calibration, your readings could drift by several decibels without you knowing. This is especially important if the meter has been stored for a while, exposed to temperature swings, or dropped.
Measuring Outdoor and Wind Noise
Wind is the biggest source of error for outdoor measurements. Moving air hitting a microphone creates turbulent pressure fluctuations that the meter interprets as sound. Research measuring wind noise at different speeds found levels of 84.9 dB at just 10 mph, climbing proportionally up to 120.3 dB at 60 mph. Even a light breeze can add enough noise to compromise a reading.
A foam windscreen (the round sponge cover that slips over the microphone) is essential for outdoor work. It breaks up the airflow before it reaches the diaphragm, reducing wind-induced noise by several decibels. Standard practice is to avoid measuring in sustained winds or precipitation altogether if the wind noise is within 10 dB of the source you’re trying to measure.
Measuring Sudden, Loud Sounds
Gunshots, fireworks, and heavy impacts produce impulsive noise that behaves differently from steady sound. These events can spike to 170 or 180 dB but last only milliseconds. Most standard sound level meters and dosimeters top out around 140 to 146 dB. When the actual peak exceeds a meter’s range, the reading gets clipped, and every metric the device calculates from that recording is compromised.
If you need to measure impulse noise accurately, you’ll need a high-end Type 1 sound level meter with a quarter-inch microphone rated for 160 dB or higher. Set the meter’s response time to “Peak” rather than “Slow” or “Fast,” and use C-weighting to capture the full force of the pressure wave.
Key Noise Limits to Know
Once you have a decibel reading, it helps to know what the numbers mean in context. NIOSH sets the recommended exposure limit for workplace noise at 85 dBA averaged over an 8-hour shift. For every 3 dB increase above that, the safe exposure time is cut in half. So 88 dBA is safe for 4 hours, 91 dBA for 2 hours, and so on.
For general environmental noise (not workplace), the EPA recommends a 24-hour average no higher than 70 dBA to prevent hearing loss over a lifetime, which translates to roughly 75 dBA over an 8-hour period. Both limits are based on the same body of scientific evidence and use the same 3 dB exchange rate. If your measurements consistently land above these thresholds, hearing protection or noise reduction measures are worth taking seriously.