How this online decibel meter works
When you press start, your browser asks for permission to use the microphone. The page then reads the raw audio with echo cancellation, noise suppression and automatic gain control switched off (where your browser allows it), works out how much energy there is in each slice of the frequency range, and applies A-weighting so the number reflects how loud the sound seems to human ears. That's the dB(A) figure used in hearing guidance and noise rules.
The level is smoothed with a 125 millisecond time constant, the same "Fast" setting a handheld sound level meter uses, and the page keeps a running minimum, maximum and energy average (Leq).
The audio never leaves your device. There's no recording, no upload and no account.
How accurate is it?
Honestly, it's a rough guide. A browser has no idea how sensitive your microphone is, so the page assumes a typical phone microphone and lets you adjust the offset. Laptop microphones, headsets and webcams can read 10 dB or more away from the truth, and some browsers still apply their own processing whatever the page asks for.
For something you can rely on, use an app that talks to the microphone directly. Decibel Meter for Android reads unprocessed microphone audio, starts from Android's published microphone specification and supports proper calibration, and adds C and Z weighting, peak levels, noise dose and recordings. There's more on this in are decibel meter apps accurate?
What do the numbers mean?
- 20Very quiet Whisper, ticking watch
- 30Quiet Quiet bedroom at night
- 40Calm Library, quiet office
- 50Moderate Light rain, fridge hum
- 60Lively Normal conversation
- 70Loud Vacuum cleaner, busy street
- 80Very loud Heavy traffic, blender
- 90Harmful Lawn mower, motorbike
- 100Dangerous Nightclub, chainsaw
- 110Extreme Front row at a rock concert, siren
- 120Pain threshold Thunderclap, jet take-off nearby
As a rule of thumb, anything under 70 dB(A) is fine for as long as you like. From about 85 dB(A), long exposure starts to put your hearing at risk, and each extra 3 dB halves the safe time. Our decibel chart has many more examples, and the noise exposure calculator works out how long you can safely stay at a given level.
Tips for a better reading
- Hold the device still, with nothing covering the microphone, pointing towards the sound.
- Take off thick cases if you can, and keep fingers away from the microphone holes.
- Wind on the microphone causes big false readings outdoors. Shelter it, or wait for a calm moment.
- Measure for at least 30 seconds and look at the average (Leq), not just the number at one moment.
- Very quiet rooms (below about 30 dB) are below what most built-in microphones can measure.
