Decibel meter

Measure sound level in three steps

1. Press Start meter and allow microphone access. Keep the microphone uncovered and pointing at the sound.
2. Choose A-weighting for noise as people hear it, or Z (flat) for the raw level, and Fast or Slow response.
3. Watch the live value and the minimum, average and maximum. If you have a real sound level meter, enter its reading to calibrate.

Two numbers: dBFS and estimated dB SPL

The microphone delivers a digital signal, and the only thing a browser can measure exactly is its level relative to full scale, in dBFS. Sound pressure level (dB SPL) is what a real sound meter reports, and turning one into the other needs the microphone’s sensitivity and the gain your operating system applies, which no website can read. This meter adds an offset to the dBFS value to give an estimated dB SPL. The default offset is 100 dB, a rough starting point that can be 10 to 20 dB off on your device. To make the estimate meaningful, place your device next to a calibrated meter (or a measurement app you trust), play a steady noise, type that meter’s reading into Calibrate and press Match. The offset is saved on this device only. Changing the microphone, its input volume or the browser’s processing invalidates the calibration.

Why browser microphones read low or flat, and what we do about it

Browsers process microphone audio for calls: automatic gain control turns quiet rooms up and loud ones down, and noise suppression removes steady noise such as fans, traffic and hum, exactly the sounds you may want to measure. Left on, they make a decibel meter almost useless. This page asks the browser to switch all three off (echo cancellation, noise suppression and automatic gain) and shows what the browser actually reports. Chrome and Firefox normally honor the request; some phones and Safari versions keep part of the processing on, and some Bluetooth headsets process audio in the headset itself. If the report says a setting is still on, treat changes in level with suspicion, and prefer the built-in microphone over a headset.

A-weighting, Z-weighting and response time

Human hearing is much less sensitive to low bass and the very top of the range than to the middle, so noise limits are almost always given in dB(A): the A-weighting filter turns down low frequencies (by about 19 dB at 100 Hz and 39 dB at 31.5 Hz) to match. Z-weighting is flat, every frequency counted equally, which shows rumble and bass that dB(A) hides. Fast response follows changes within about an eighth of a second and is good for speech and passing cars; Slow averages over about a second and is easier to read for steady noise. The average shown is the energy average over the session (Leq), not a simple mean of the numbers, which is how noise exposure is normally summarized. Our A-weighting filter follows the IEC 61672 curve within 0.2 dB up to 4 kHz and reads up to about 1.3 dB high around 10 kHz, which hardly matters next to the uncertainty of an uncalibrated microphone.

Typical levels, for orientation

Commonly quoted rough values in dB(A): a quiet bedroom at night is around 30, a quiet office 40 to 50, normal conversation at one meter about 60, a busy road 70 to 80, a lawn mower or blender 85 to 90, and a rock concert or a nightclub 100 or more. At work, the EU noise directive (2003/10/EC) sets action values of 80 and 85 dB(A) averaged over an eight-hour day, and the US NIOSH recommends 85 dB(A) as its eight-hour limit; long exposure above that can damage hearing. Phone microphones themselves limit loud readings: above roughly 90 to 110 dB SPL they distort or compress, so very loud sounds read lower than they are. If the maximum reading sits at the same high value or the clipping warning appears, the microphone has hit its ceiling. For a hearing check rather than a room measurement, try the hearing age test.