Decibels and sound level meters, explained
A decibel (dB) is a logarithmic unit: every 10 dB means ten times more sound energy and sounds roughly twice as loud, while +3 dB already doubles the energy. Sound pressure level is measured relative to 20 micropascals, the quietest sound a young ear can hear (0 dB). A quiet room is around 30 dB, conversation 60 dB, a busy street 70 to 80 dB, and from about 85 dB long exposure starts to damage hearing. This online decibel meter turns the signal of your microphone into these levels with the same filters and averages a professional meter uses.
dBA, dBC and dBZ
Our ears are less sensitive to low and very high frequencies. A-weighting follows that curve and is what workplace rules, noise ordinances and most limits are written in. C-weighting is almost flat and keeps the bass, so it is used for peaks and for music venues where bass matters. Z-weighting means no filter at all. The A and C filters here follow the pole frequencies of the IEC 61672 standard and are normalised to 0 dB at 1 kHz.
Fast, slow and Leq
The instant level depends on the time weighting: Fast (125 ms) follows quick changes such as speech, Slow (1 second) smooths them out. Because noise goes up and down, a single number for a period is the equivalent continuous level, Leq: the steady level that would carry the same total energy. One loud minute raises the Leq of an hour far more than you would guess, because of the logarithmic scale. The percentiles add context: L90 is the background level exceeded 90% of the time, L10 the level of the loudest moments.
Safe listening and the noise dose
| Level (dBA) | Safe daily time (NIOSH) | Example |
|---|
| 85 | 8 hours | Heavy traffic, food blender |
| 88 | 4 hours | Motorbike at a few metres |
| 91 | 2 hours | Lawn mower, power drill |
| 94 | 1 hour | Loud bar or gym class |
| 100 | 15 minutes | Nightclub, concert |
| 110 | 1.5 minutes | Front row of a rock concert |
The dose meter adds up your exposure with the NIOSH rule (85 dBA for 8 hours, halve the time per 3 dB). 100% means you reached the recommended daily limit. European workplace rules (Directive 2003/10/EC) use 80 and 85 dBA as action values and an 87 dBA limit, also with a 3 dB exchange rate.
How accurate is a phone or browser decibel meter?
Without calibration expect an error of about 5 to 10 dB, because every microphone, sound card and operating system has a different sensitivity, and some phones still apply automatic gain. Relative changes (is it louder than yesterday, which machine is noisiest) are reliable straight away. For absolute numbers, calibrate once against a class 1 or 2 sound level meter or a calibrator; the offset is saved in your browser for next time. Very loud sounds can clip the microphone, which the meter warns about. For legal or occupational measurements, use a certified meter.
Privacy
The microphone signal is processed in real time inside this browser tab with the Web Audio API and thrown away; only the levels are kept, and only until you reset or close the page. Nothing is recorded, stored on a server or sent anywhere.