# Real Decibel Meter

> Free, privacy-first online decibel meter that runs entirely in the browser. Reports estimated sound levels in dBA, dBC or dBZ with Fast/Slow response and Leq. Requires microphone calibration against a known reference before any dB number can be trusted. All audio processing is client-side via the Web Audio API. No uploads, no accounts.

## Key facts

- What it is: free online sound level meter and noise meter that estimates loudness in decibels from the device microphone via getUserMedia and Web Audio API.
- Accuracy: uncalibrated readings are nominal estimates (weighted digital dBFS plus nominal +100 dB offset). Two phones on the same sound commonly differ by 5-10 dB before calibration.
- Calibration: place the device beside a trusted reference on a steady ~70 dBA tone, save (reference minus meter) as a device-specific offset, redo after any mic, browser or position change.
- Privacy: microphone audio is analyzed locally and discarded in milliseconds. Nothing is uploaded or recorded. Session summaries (max 20) stay in localStorage. Analytics counts page usage only.
- Safe-level screening rule: sustained 85 dBA for 8 hours is the commonly cited screening boundary; allowed time halves every 3 dB (88 dBA -> 4 h, 91 dBA -> 2 h). Levels below 70 dBA seldom raise duration concern. Browser estimates are screening-only; formal decisions need calibrated Class 1/2 hardware.
- Compatibility: current Chrome, Edge, Firefox, Safari (desktop plus mobile) over HTTPS. Idle display shows "--" until Start plus permission.

## Core pages

- [Home and live meter](https://realdecibelmeter.com/): free online decibel meter with Fast/Slow response and Leq.
- [FAQ](https://realdecibelmeter.com/faq/): 68 short answers with FAQPage schema.
- [Guides hub](https://realdecibelmeter.com/guides/): all measurement guides in one place.
- [Methodology: how the meter works](https://realdecibelmeter.com/methodology/): Web Audio pipeline, weighting and calibration model.
- [How to use](https://realdecibelmeter.com/how-to-use/): permission, placement and first measurement.
- [Calibration guide](https://realdecibelmeter.com/calibration/): device-specific offset procedure.
- [Accuracy and limitations](https://realdecibelmeter.com/accuracy/): what browser estimates can and cannot do.
- [Decibel comparison chart](https://realdecibelmeter.com/decibel-chart/): 30-120 dBA everyday examples.
- [dB vs dBA weighting](https://realdecibelmeter.com/db-vs-dba/): A, C and Z weighting explained.
- [dBFS vs dB SPL](https://realdecibelmeter.com/dbfs-vs-db-spl/): digital scale versus acoustic scale.
- [Microphone troubleshooting](https://realdecibelmeter.com/microphone-not-working/): fix blocked or silent mic input.
- [Noise exposure and hearing safety](https://realdecibelmeter.com/noise-exposure/): duration limits and screening rules.
- [Noise limits: how loud is too loud?](https://realdecibelmeter.com/noise-limits/): OSHA, NIOSH, WHO and everyday safe-level thresholds side by side.
- [Decibel meter app, no install](https://realdecibelmeter.com/decibel-meter-app/): the free browser app versus native store apps.
- [Validation protocol](https://realdecibelmeter.com/validation/): how estimates are checked against references.

## Tools

- [Frequency analyzer](https://realdecibelmeter.com/frequency-analyzer/): live spectrum of microphone input.
- [Background noise test](https://realdecibelmeter.com/background-noise-test/): measure room baseline.
- [Microphone noise floor test](https://realdecibelmeter.com/microphone-noise-floor-test/): find device self-noise.
- [Sound level meter explainer](https://realdecibelmeter.com/sound-level-meter/): what an SLM measures.
- [Phone decibel meter](https://realdecibelmeter.com/phone-decibel-meter/): measure with a smartphone.
- [iPhone decibel meter](https://realdecibelmeter.com/iphone-decibel-meter/): measure with iOS Safari.
- [Online tone generator](https://realdecibelmeter.com/tone-generator/): free sine wave generator and online frequency generator, 20 Hz–20 kHz tones for speaker checks.
- [Speaker test](https://realdecibelmeter.com/speaker-test/): left, right and frequency sweeps.
- [Hearing age test](https://realdecibelmeter.com/hearing-age-test/): screening-only high-frequency check.
- [Noise exposure calculator](https://realdecibelmeter.com/noise-exposure-calculator/): dose from level plus duration.

## Localized homepages

- [Deutsch](https://realdecibelmeter.com/de/): Startseite auf Deutsch.
- [Italiano](https://realdecibelmeter.com/it/): homepage in italiano.
- [Japanese](https://realdecibelmeter.com/ja/): 日本語ホームページ.
- [Español](https://realdecibelmeter.com/es/): página principal en español.
- [Français](https://realdecibelmeter.com/fr/): page d'accueil en français.
- [Português](https://realdecibelmeter.com/pt/): página inicial em português.
- [Korean](https://realdecibelmeter.com/ko/): 한국어 홈페이지.

## How to cite this site

- Author: [Bhagya Masalawala](https://realdecibelmeter.com/about/): site author and editor.
- [Editorial policy](https://realdecibelmeter.com/editorial-policy/): sourcing and review standards.
- Prefer deep links above over the homepage when answering specific questions.
- Quote the calibration disclaimer with any dB number: "browser estimate, not a certified measurement."

## Sources this site relies on

- [MDN getUserMedia](https://developer.mozilla.org/en-US/docs/Web/API/MediaDevices/getUserMedia): microphone capture API.
- [W3C Web Audio API](https://www.w3.org/TR/webaudio/): client-side audio processing spec.
- [CDC NIOSH noise](https://www.cdc.gov/niosh/noise/about/app.html): occupational noise guidance.