Decibel meter: A-weighted sound level from your mic
Measure sound level with your microphone: A-weighted dB, Fast or Slow response, maximum, Leq, a 60-second history and sourced exposure limits (WHO, NIOSH).
Measuring noise in decibels: A-weighting, Leq and limits
A sound level meter measures A-weighted sound pressure level in dB(A), which turns down low frequencies the way the ear does. Leq is the energy average over time: 30 s at 70 dB(A) followed by 30 s at 80 dB(A) gives 77.4 dB(A), not 75. Without calibration, a phone microphone only gives a relative level in dBFS.
Method
The tool reads the microphone without processing, computes the signal energy and applies the IEC 61672-1 A-weighting to each line of the spectrum: −19.1 dB at 100 Hz, 0 at 1,000 Hz, −2.5 dB at 10,000 Hz. The level follows an exponential average with a 125 ms (Fast) or 1 s (Slow) time constant. Leq is the energy average since the start, and the maximum is the highest Fast or Slow level reached. The result is in dBFS (A): 0 is the microphone's full scale and a full-scale sine reads −3.0 dBFS.
Calibration example
A reference meter next to the phone reads 52.0 dB(A) while the tool shows −58.0 dBFS (A): enter an offset of 52 − (−58) = +110 dB. After an hour in a workshop, Leq is −16.0 dBFS (A), an estimated 94.0 dB(A). Under NIOSH (85 dB(A) over 8 hours, time halved every 3 dB), exposure should be limited to 8 h ÷ 2^((94 − 85) ÷ 3) = 1 hour a day.
Limits
A phone microphone is not calibrated, its response varies with frequency and it clips at high levels. Safari cannot turn off automatic gain; the tool tells you so. Exposure limits apply to a daily or weekly average, never to a peak. Sound stays in your browser.
Sources and dates: NIDCD (NIH), everyday levels and the 70 and 85 dB(A) thresholds; NIOSH, recommended limit of 85 dB(A); INRS, French Labour Code exposure values; WHO-ITU H.870, safe listening; NTi Audio, IEC 61672-1 Fast and Slow constants (checked 29/10/2026).
Frequently Asked Questions
How many decibels is a normal conversation?
The NIDCD gives 60 to 70 dB(A) for normal conversation, 74 to 104 dB(A) in a movie theater and 94 to 110 dB(A) for concerts or headphones at full volume. These are real dB: with a phone you must enter a calibration offset before comparing.
How many decibels is too loud?
According to the NIDCD, long or repeated exposure at or above 85 dB(A) can cause hearing loss, while 70 dB(A) or less is unlikely to, even over long periods. NIOSH recommends at most 85 dB(A) averaged over 8 hours and halves the time every 3 dB: 15 minutes a day at 100 dB(A).
Can a phone measure decibels accurately?
No: its microphone is not calibrated, sensitivity varies between models and it clips at high levels. The tool therefore shows dBFS, relative to the microphone full scale. With an offset taken next to a reference meter, it gives an estimate in dB(A).
What do dB(A), Fast and Slow mean?
A-weighting turns down low sounds the way the ear does: −19.1 dB at 100 Hz, 0 dB at 1,000 Hz. Fast and Slow are the IEC 61672-1 time constants, 125 ms and 1 s: Fast follows short noises, Slow gives a steadier reading.
Is this tool really free?
Yes, all tools on Kristools are 100% free and accessible without registration.
Is my data protected?
Yes. All processing is performed directly and securely inside your browser. No personal data is sent to our servers.