Methodology

How this meter measures sound.

Every number this tool shows comes from your device's microphone and a short chain of arithmetic. This page documents that chain, and is equally clear about where it stops being trustworthy.

From microphone to decibels

The browser's Web Audio API hands the page a stream of raw audio samples, each a number between −1 and 1 representing instantaneous air pressure. For every analysis frame the tool computes the root mean square of those samples — square each one, average them, take the square root. RMS is used rather than a simple average because sound waves swing symmetrically around zero and would otherwise cancel out to nothing.

That RMS amplitude is converted to a decibel value with the standard logarithmic formula, dB = 20 × log₁₀(RMS / reference), then offset into the range a sound level meter reports. The scale is logarithmic, so a 10 dB rise is roughly ten times the sound intensity and about twice the perceived loudness.

A-weighting and C-weighting

Human hearing is not equally sensitive across frequencies — we hear a 1 kHz tone far more readily than a 50 Hz one at the same pressure. Weighting curves correct for that.

dBA applies A-weighting, which discounts low frequencies steeply to approximate how the ear responds. It is what occupational limits are written in, and it is the mode to use for almost everything. dBC applies far less correction and stays close to flat across the audible range, which makes it the right choice for bass-heavy music, machinery, and other low-frequency sources that A-weighting would understate.

Why the reading is approximate

Expect this tool to land within roughly ±2–3 dB of a calibrated meter under ordinary conditions. Three things account for the gap:

• Uncalibrated microphones. Phone and laptop microphones are tuned for speech intelligibility, not measurement, and no two models respond identically.
• Browser audio processing. Automatic gain control, echo cancellation, and noise suppression are designed to make voices clearer, which is the opposite of what a meter wants. The tool disables these where the browser allows it, but support varies.
• The upper and lower ends. Very quiet rooms sit near the noise floor of the hardware, and very loud sources clip the input. Readings compress at both extremes.

Where this tool is not enough

A browser reading is genuinely useful for trend monitoring, comparing one room to another, checking whether a space is getting louder, and building intuition about the scale. It is not a substitute for certified equipment.

Any legally consequential measurement — an OSHA hearing-conservation assessment, a noise-ordinance complaint intended to stand up, an occupational exposure record — requires a sound level meter built and verified to IEC 61672-1, the standard that defines Class 1 (precision, ±1.1 dB at 1 kHz) and Class 2 (general purpose, ±1.4 dB at 1 kHz) instruments. Those meters are also field-calibrated against a reference source before use. A phone microphone is neither built nor calibrated to that specification, and no amount of software can make it so. If you need to know how long a given level is safe for, the exposure limit calculator applies both the OSHA and NIOSH rules.

Privacy

All of the above happens on your device. Audio samples are analysed in the page and discarded frame by frame. Nothing is recorded, stored, or transmitted — there is no server to send it to.