Online Decibel Meter — free sound level meter in your browser

Yes. There is no account, no subscription, no free trial, no paid tier, no advertising and no app to install. The page is a single HTML file that runs entirely in your browser. The only analytics is SimpleAnalytics, which is cookie-free and records no personal data.

The frequency weighting is accurate; the absolute level is only as good as your calibration. The A- and C-weighting filters here match the IEC 61672 curves to within 0.35 dB from 16 Hz to 4 kHz and 0.85 dB at 8 kHz, rolling off about 3 to 4 dB early at 16 kHz.

What no browser can know is how many dB SPL correspond to a full-scale digital signal on your particular microphone — that depends on the capsule, the preamp gain and the driver, none of which are exposed to a web page. So the absolute reading starts as an estimate until you set the calibration offset. Once calibrated against a reference, repeat measurements on the same device are consistent and genuinely useful. Do not use any browser meter for legal, medical or workplace-compliance decisions.

Because automatic gain control defeats sound level measurement: it raises the microphone gain when a room is quiet and lowers it when the room is loud, which is precisely the variation you are trying to measure. This meter requests the microphone with autoGainControl, noiseSuppression and echoCancellation set to false, then reads back what the browser actually applied and shows it on screen. If your browser refuses to disable them, the readings are compressed and the meter says so instead of pretending otherwise.

They are frequency weightings. A-weighting discounts low and very high frequencies to approximate human hearing sensitivity at moderate levels, and it is what almost every noise regulation and hearing-protection guideline is written in. C-weighting is much flatter and keeps bass energy, so it is used for peak measurements and low-frequency problems like club bass or plant rumble. Z is unweighted — the raw level with no filter. When a rule or an app just says "decibels", it almost always means dBA.

LAeq is the equivalent continuous level: the single steady A-weighted level that carries the same total sound energy as the whole varying measurement. It is the number noise surveys and regulations quote, and it is not the same as averaging the displayed readings.

LAFmax and LAFmin are the highest and lowest A-weighted levels seen with Fast time weighting. LCpeak is the true peak pressure of the C-weighted signal, sampled at full audio rate rather than smoothed — which is why it reads much higher than the displayed level on impulsive sounds like a door slam or a hammer blow.

Statistical percentiles of the measured level. L10 is the level exceeded 10% of the time, characterising the intrusive peaks; L50 is the median; L90 is the level exceeded 90% of the time, the usual proxy for the residual background once traffic, voices and other events are taken out. Environmental noise assessments lean on them heavily, because a single average hides whether a place is steadily noisy or mostly quiet with occasional bangs.

Put this meter next to a reference you trust — a calibrated sound level meter, or an acoustic calibrator producing 94 dB at 1 kHz — expose both to the same steady sound, type the reference's reading into the calibration box and press match. The meter solves for the offset and stores it in your browser for that device, so it persists between visits. With no reference at all, leave the default: readings stay internally consistent for comparing one place with another on the same device, they simply are not absolute.

Yes — press F, click the reading itself, or use the Fullscreen button in the Controls panel. The level fills the screen with the gauge and the LAeq, LAFmax, LCpeak and percentile tiles underneath, big enough to read across a workshop, studio, classroom or meeting room. Esc exits, or move the mouse and click Exit fullscreen. If a browser refuses the fullscreen request — iOS Safari on iPhone does — the page falls back to filling the browser window, so the big readout still works.

No. The microphone stream is processed by the Web Audio API inside your browser tab; nothing is written to disk or sent anywhere, and there is no server component to send it to. Closing the tab discards everything. The only things stored locally are your calibration offset and display preferences.

Yes — the page works in mobile browsers with microphone permission. Phone microphones are often better behaved than laptop ones, simply because they are not sitting behind a keyboard and a cooling fan. They do tend to limit and compress at high levels though, so a phone will usually under-read loud sources such as concerts and power tools. Calibrate on the device you intend to use, and treat anything above roughly 100 dB as approximate.

NIOSH recommends a limit of 85 dBA averaged over an eight-hour day, halving the allowed time for every 3 dBA above that — roughly 8 hours at 85 dBA, 1 hour at 94 dBA, 15 minutes at 100 dBA. The enforceable US OSHA standard is more permissive: 90 dBA over eight hours with a 5 dB exchange rate. For homes rather than workplaces, the WHO's 2018 European guidelines recommend keeping road traffic noise below 53 dB L_den and below 45 dB L_night.