Short answer: To measure decibels, open a sound level meter or a free online decibel meter, allow the microphone, hold the device at ear height about an arm’s length from your body, set it to dB(A), and read the average (Leq) over 30–60 seconds. Calibrate a phone once against a known source for results within a few decibels.
This is our complete guide to sound measurement. It compares the five practical methods, explains exactly how to take a reliable reading in a room, outdoors, from an appliance or over a whole night, and shows how to read the numbers. Everything here works with the free sound decibel meter on our homepage.
5 Ways to Measure Decibels
| Method | Best for | Typical accuracy | Cost |
|---|---|---|---|
| Online decibel meter in your browser | Quick checks on phone or computer, no install | ±2–5 dB once calibrated (about 40–100 dB) | Free |
| Phone app | Offline use, extra features | Similar to a browser meter; depends on the microphone | Free to paid |
| Built-in phone or watch features | Background alerts, headphone levels | Good for trends, not exact readings | Free with the device |
| Sound level meter (Class 2 or Class 1) | Workplace, legal or professional reports | ±1–1.5 dB (Class 2) or better (Class 1) | From about $100 to thousands |
| Noise dosimeter or long-term logger | Personal exposure over a work shift; noise complaints | Class 2 or better | Professional |
For a detailed comparison, see online decibel meter vs app and sound level meter vs decibel meter.
Step by Step: Measure Decibels Online
- Open the sound decibel meter in Chrome, Edge, Safari or Firefox and press Start.
- Allow microphone access. If the level doesn’t move, check the input device with the microphone test.
- Choose dB(A) for general noise (dB(C) for bass or music) and Slow response for steady noise.
- Hold the device where the listener’s ears are, microphone pointing at the source, at least an arm’s length from your body.
- Wait 30–60 seconds and note the average (Leq) and the maximum. Save the result with the CSV or report image if you need a record.
How to Position the Microphone
- Height: ear height, about 1.2 m seated or 1.5–1.6 m standing.
- Distance: at least 1 m from walls and large objects, which reflect sound and add a few decibels.
- Your body: hold the device away from you or put it on a stand; your body blocks and reflects sound.
- Fingers and cases: keep them away from the microphone opening (on phones it is usually on the bottom edge).
- Wind: outdoors, even a light breeze causes false low-frequency readings; shield the microphone or use a foam windscreen.
How to Measure Noise in a Room
- Close windows and doors as they normally are, and switch off sources you don’t want to include.
- Measure at three or more positions where people sit or sleep, each for at least 30 seconds.
- Average the readings on an energy basis with the decibel calculator (not a simple arithmetic average).
- Check the empty room’s background level with the background noise test, then compare with the targets in room noise levels.
Measuring Noise Over Time
Traffic, neighbours and workplaces change from minute to minute, so a single reading can mislead. Log the level instead: the noise monitor records every second for up to 24 hours, even in a background tab, and reports Leq (average), L10 (peaks), L90 (background) and every event above your limit. That is the evidence you need for a complaint (see apartment noise complaint levels) or a workplace check with the noise exposure calculator.
Measuring Appliances, Speakers and Headphones
- Appliances: measure at 1 m in front of the machine at ear height, then again where you usually are. Manufacturers often quote sound power, which isn’t the same as the level you measure.
- Speakers and music: measure at the listening position. For the loudness of a recording rather than playback level, use the audio loudness meter (LUFS).
- Headphones: a microphone held near the ear cup gives only a rough idea; accurate headphone measurement needs an ear simulator.
On a Phone: iPhone and Android
Phones make good pocket meters because their microphones are designed for speech in the range where most everyday noise sits. Open the online meter in Safari or Chrome, allow the microphone when asked, and keep the phone’s bottom edge (where the main microphone usually is) pointed at the source. Turn off any voice isolation or noise suppression feature for calls and recordings if your phone has one, because it lowers the measured level. Many phones and smartwatches also warn about loud surroundings or headphone levels in the background; those alerts are useful for spotting trends but don’t replace a measurement.
On a PC, Mac or Laptop
On a computer, the meter uses the selected input device, which may be the built-in laptop microphone, a webcam or a USB microphone. Choose the right input in your browser’s site permissions and in the system sound settings, and disable “enhancements”, automatic gain control or noise cancellation where the settings allow it. Keep the laptop away from its own fan noise, or use an external USB microphone on a stand. A desktop microphone is often steadier than a phone held in the hand, which makes it a good choice for long room measurements.
Outdoors and at Work
- Traffic and construction: measure at the façade or window you care about, 1.2–1.5 m above the ground, for at least 10–15 minutes, and note the time of day. Traffic noise varies a lot, so an average (Leq) is essential.
- Workplaces: measure at the worker’s ear position during a typical task, then estimate the whole shift. Workplace limits are 8-hour averages; see the NIOSH and OSHA limits.
- Events and venues: measure where the audience stands, not next to the speakers, and average over at least 15 minutes, the period used by the WHO safe listening venue standard.
Which Settings to Use
| Setting | Choose | Why |
|---|---|---|
| Frequency weighting | A for most noise; C for bass, music and peaks; Z for analysis | A-weighting matches hearing; see dBA vs dBC |
| Time weighting | Slow (1 s) for steady noise; Fast (125 ms) for changing noise | Slow is easier to read; Fast follows speech and music |
| Result to report | Leq plus Lmax | Regulations and exposure limits use the average |
Calibrate for Better Accuracy
Every phone and laptop microphone has a different sensitivity, and operating systems can apply gain control or noise suppression. Calibration corrects the offset: compare with a sound level meter or a 94 dB calibrator and enter the difference once. The guide to calibrating your microphone shows three ways, and online decibel meter accuracy explains what to expect. Browser meters are most reliable between about 40 and 100 dB; very quiet rooms hit the microphone’s noise floor, and very loud sounds above about 110–120 dB can overload it.
Reading Your Measurement
- Leq: the average level with the same energy over the measurement; the most useful single number.
- Lmax: the loudest moment; important for sleep disturbance.
- Peak: the highest instantaneous pressure; important for bangs and impacts.
- What the number means: 30–40 dB is quiet, 60 dB is conversation, 85 dB(A) is the level where long exposure risks hearing. Look up any level on the decibel chart or in the safe noise levels chart.
Common Measurement Mistakes
- Taking one quick reading instead of an average.
- Holding the phone against your body, in a pocket or next to a wall.
- Measuring outdoors in wind without shielding the microphone.
- Comparing an unweighted reading with a limit that is in dB(A).
- Leaving noise suppression or “voice isolation” switched on, which lowers the reading.
- Trusting readings above about 110 dB from a phone (they are usually too low).
When You Need a Professional Measurement
For workplace compliance, planning applications, legal disputes or building acoustics tests, use a certified Class 1 or Class 2 sound level meter operated by a trained person. A browser meter is ideal for everyday checks, screening and gathering initial evidence. It can also show whether a professional survey is worth paying for.
Frequently Asked Questions
How can I check the decibel level without an app?
Use an online decibel meter in your browser: open it, allow the microphone and read the level. It works on phones, tablets and computers.
How accurate are phone decibel meters?
Usually within 2–5 dB of a sound level meter in the everyday range after calibration; less accurate for very quiet or very loud sounds.
What is the best way to measure noise from neighbours?
Log the level in the affected room over the problem period, keep a diary of times and sources, and compare with local limits.
Should I use dB or dBA?
Use dBA for loudness, comfort and safety; see dB vs dBA for when the difference matters.
Addito is an audio analysis and sound measurement writer specializing in decibel testing, noise level analysis, sound frequency measurement, and audio engineering tools for creators, audio professionals, students, and everyday users. He creates practical content focused on sound measurement, hearing safety, microphone testing, and acoustic analysis tools.