Decibel Meter Online

How accurate is an online decibel meter?

The dBFS figure is exact; the dB figure is an estimate until you calibrate. dBFS measures the digital signal your browser delivers, while dB of sound pressure depends on the microphone's sensitivity, which no browser reports — so the meter adds an offset, 90 dB by default, which is a round guess rather than a property of your device.

To calibrate, put a real sound level meter (or an app you trust) next to your phone or laptop, let both run for a few seconds in steady noise, type its reading and press Match this reading. The meter takes the energy average of the last 3 seconds and sets the offset so the two agree. The offset is kept in this browser; calibrate again after switching microphone or browser.

What the meter does

• Raw microphone. It asks the browser to switch off echo cancellation, noise suppression and automatic gain, and shows whether the browser obeyed. Automatic gain would lift quiet rooms and turn loud ones down.
• Time weighting. Fast (0.125 s) and Slow (1 s), the two exponential time constants of IEC 61672-1, the sound level meter standard. About 60 times a second the meter reads the latest 2,048 samples (43 ms at 48 kHz) and feeds their mean square into that average.
• Average (Leq). An energy average — the mean of the squared signal over the session, converted to decibels — not the average of the numbers on screen. Minimum and maximum are of the time-weighted level; the first half second is skipped while it settles.
• A-weighting. The IEC 61672-1 A-curve, built as three filters in your browser. Checked against the standard's table at 48 kHz it reads −19.17 dB at 100 Hz (standard −19.1), 0 at 1 kHz and −1.9 at 10 kHz (standard −2.5): within 0.8 dB from 20 Hz to 10 kHz at 44.1 and 48 kHz. Above 10 kHz it falls off faster, −3.1 dB too low at 16 kHz. Flat (Z) applies no weighting.
• The chart shows the last 60 seconds, one point every 0.1 s.

Typical sound levels

The US National Institute on Deafness and Other Communication Disorders (NIDCD) lists these average levels on its Noise-Induced Hearing Loss page (updated April 2025), and states that sounds at or below 70 dBA are unlikely to cause hearing loss even after long exposure, while long or repeated exposure at or above 85 dBA can.

Honest limits

• Phone and laptop microphones are not measuring instruments. Their frequency response is not flat and the meter does not correct it, so the A-weighting is applied to an already coloured signal.
• The loudest reading possible is the offset itself: at 0 dBFS the microphone's digital signal is full, and anything louder reads the same. With the default offset that ceiling is 90 dB.
• The operating system or the microphone may still process the sound even when the browser reports processing off.
• This is not a substitute for a workplace or legal noise measurement. Nothing is recorded or uploaded.