A free decibel meter that runs in your browser
This decibel meter turns your phone’s or computer’s microphone into a simple sound level meter. Press start and it shows how loud your surroundings are in decibels, with a needle gauge, the minimum, average and maximum, and a chart of the last minute — useful for checking a noisy neighbour, a classroom, an open-plan office, a baby monitor or the volume of your music.
It works like a basic hardware meter: you can choose A, C or Z frequency weighting and fast or slow response, and enter a calibration offset so the readings match a proper meter. Nothing is recorded or uploaded; the sound is analysed in your browser and thrown away.
Be realistic about accuracy. A phone microphone is not a calibrated instrument, so treat the numbers as an estimate (and a good tool for comparisons) unless you calibrate against a real meter.
How to use the Decibel Meter
- Press Start measuring and allow microphone access when your browser asks.
- Hold the phone or laptop still, with the microphone pointing at the sound and nothing covering it. Keep your fingers and voice away from it.
- Read the live level, and watch Min, Average (Leq) and Max build up. Press Reset min/avg/max to start a new measurement.
- Choose A weighting for noise and hearing risk, C for loud music and bass, and Z for an unweighted reading. Use Slow for a steadier needle.
- To calibrate, place a trusted sound level meter next to the microphone, type its reading and press Match this reading.
Decibel Meter features
Real weighting filters
The A and C curves of IEC 61672 are built as digital filters for your device’s sample rate and stay within about 1 dB of the standard from 20 Hz to 16 kHz.
Fast and slow response
Exponential time weighting with the standard 125 ms (Fast) and 1 s (Slow) time constants, as on hardware meters.
Leq, min, max and peak
The average is the energy-equivalent level (Leq), not a simple mean of readings. Peak shows the highest sample in dBFS and warns when the input clips.
Raw microphone input
The meter asks the browser to switch off echo cancellation, noise suppression and automatic gain, which would otherwise distort levels.
Saved calibration
Your offset is stored in this browser, so a calibrated phone stays calibrated next time.
Live chart and reference table
The last 60 seconds are plotted with an 85 dB guide line, and the matching row of the typical-levels table lights up.
How the decibel reading is calculated
The microphone signal passes through the chosen weighting filter, then its squared value is averaged with the Fast or Slow time constant. That gives a level in dBFS — decibels relative to the loudest signal the microphone can deliver, where a full-scale sine wave is 0 dBFS. Because the browser cannot know how many pascals of pressure equal 0 dBFS on your device, the meter adds an offset (100 dB by default) to estimate sound pressure level: dB = dBFS + offset.
Calibrating sets that offset properly. A 94 dB acoustic calibrator or a Class 1 or Class 2 meter beside the phone gives the best result; re-calibrate if you change device, browser or microphone.
Safe listening limits
The US National Institute for Occupational Safety and Health (NIOSH) recommends limiting exposure to 85 dB(A) averaged over eight hours. Each 3 dB increase doubles the sound energy, so the safe time halves:
| Level dB(A) | Recommended maximum per day |
|---|---|
| 85 | 8 hours |
| 88 | 4 hours |
| 91 | 2 hours |
| 94 | 1 hour |
| 97 | 30 minutes |
| 100 | 15 minutes |
| 103 | 7.5 minutes |
Getting a more reliable measurement
- Do not cover the microphone and do not hold the phone close to your body; reflections and handling noise change the reading.
- Phones may have several microphones; pointing the bottom edge at the source usually works best.
- Very loud sounds can overload a phone microphone. If “input is clipping” appears, the true level is higher than shown.
- For checking your microphone itself, use the mic test; for hearing comfort, try the hearing test.
- These readings are informational only and are not a substitute for a certified meter in workplace, legal or medical assessments.
Decibel Meter FAQ
How accurate is this online decibel meter?
Uncalibrated, expect errors of 5–10 dB or more, because microphones differ. After calibrating against a real meter, readings are usually within a few decibels for everyday noise, but it is still not a certified instrument.
What is the difference between dB(A) and dB(C)?
A-weighting reduces low and very high frequencies the way human hearing does at moderate levels; it is used for noise and hearing-risk limits. C-weighting is almost flat and keeps more bass, so it is used for loud music and peak measurements.
How loud is too loud?
Long exposure above 85 dB(A) can damage hearing. At 100 dB(A) the recommended limit is about 15 minutes a day. Wear ear protection at concerts and when using loud tools.
Why does my phone show a lower reading than a real meter?
Phones apply their own processing and their microphones lose sensitivity at very low and high frequencies. Use the calibration field to add the difference.
Is my audio recorded or sent anywhere?
No. The sound is measured in real time in your browser and discarded. Nothing is stored except your calibration offset.
Can I use it to measure my neighbour’s noise?
It is useful for keeping your own log of how loud and how often, but a complaint to a council or landlord may need measurements from a certified meter.