What Is a Sound Level Meter?

One job, three common names

A decibel meter reports how intense the sound in the air is, in decibels. Engineers tend to say sound level meter, the public often says noise meter or dB meter, and an online sound meter is the same function running in a browser. For everyday checks the terms are interchangeable: place the microphone where you want to measure, allow access, and read the live dB value. The scale behind the number is covered in the decibel comparison chart, and the weightings in dB vs dBA.

Hardware meters and their classes

Dedicated hardware meters are built around calibrated capsules with documented frequency response, and certified models meet tight tolerances as Class 1 or Class 2 instruments with periodic laboratory calibration. They log defensible Leq values for assessments, pair with acoustic calibrators that emit a known tone, and produce reports a regulator or court accepts. That chain of traceability is the entire point of the hardware — and the part no consumer microphone can reproduce.

What a browser meter does instead

A browser meter reuses the microphone you already own: the page captures audio through the Web Audio API, reduces each block to RMS, converts to a level in dB, applies the selected A, C or Z weighting with Fast or Slow response, and accumulates Leq — all locally on your device. Before calibration it shows a clearly labelled nominal estimate from a default offset; a saved profile replaces that default with your reference-derived offset. The exact pipeline is documented in how measurement works, and its boundaries in accuracy and limitations.

When each one fits

• Browser meter: room checks, speaker tests, before-and-after comparisons, classroom curiosity, finding the loudest appliance — see how to use and phone measurement.
• Certified hardware: workplace compliance, legal evidence, planning applications, hearing-safety certification — with the repeatability discipline in the validation protocol.
• Either way, exposure thinking needs duration plus Leq, not a single peak — see noise exposure.

Inside every meter: capsule, weighting, detector, display

Strip any sound level meter to four blocks. The capsule turns air motion into voltage; the weighting shapes that signal to mimic hearing (A for everyday levels, C for heavy peaks, Z for flat); the detector smooths it with Fast at 125 ms or Slow at 1 second; the display reports current level plus Leq, minimum and maximum. This site mirrors that chain: mono audio through the Web Audio API with getUserMedia over HTTPS, reduced to RMS, A, C or Z from the dominant band, Leq accumulated locally. The spectrum is display only, idle shows "--", input never reaches speakers, and permission is asked once per origin.

Before you calibrate, the readout is a labelled estimate: weighted dBFS plus a nominal +100 dB offset, with raw dBFS visible in Digital Diagnostics. A saved profile replaces that default with your own device-specific correction.

Run a reading you can repeat next week

Pick one question — "how loud is the bedroom at midnight" — and freeze everything else. Stand the microphone where ears actually are, note the distance to the source, choose A-weighting with Slow response, and stay silent for 30 to 60 seconds. Read the Leq, not a flickering instant: a fridge at 1 metre might swing between 38 and 44 dBA yet settle near 41 dBA Leq.

• Compare against a known reference at the same spot to build your offset, then redo it whenever the setup changes — case, phone, browser version or headset.
• Never copy an offset across devices; two models on the same sound commonly sit 5 to 10 dB apart before correction.
• Keep the last 20 sessions stored locally for before-and-after checks, and export CSV or JSON only once calibrated — see calibration and how to use.

Read the result without fooling yourself

You get five numbers per run: current, minimum, Leq, maximum and duration, drawn as a 240-point graph. Ignore the decimal place; round to the nearest whole decibel and watch the Leq line. Below about 30 dBA most consumer capsules read high on their own noise floor, above roughly 95 to 100 dBA they clip and read low, and deep bass arrives under-reported. Levels under 70 dBA accept a full day without a second thought, while 85 dBA allows around 8 hours with allowance halving every 3 dB — screening only, per noise exposure. Anything needing proof belongs on a Class 1 or Class 2 instrument, as described in dBFS vs dB SPL.

Open the online decibel meter → · Frequency analyzer → · Common questions →