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Online Decibel Meter — Free Tool

Free online decibel meter showing live dBFS levels with Fast/Slow ballistics and peak hold. Relative readings, not calibrated SPL. Runs in your browser.

Protect your hearing. Start at a low volume. Never raise the volume to make a tone audible. Levels are shown in dBFS, relative to full scale — not SPL.

How it works

Raw microphone audio with IEC 61672-1 Fast/Slow ballistics and dBSPL calibration. Audio is analyzed in local memory with zero server transmission or storage.

Monitoring ambient sound levels is critical for protecting hearing health, evaluating acoustic treatments, and ensuring safe working environments.

How Browser Acoustic Measurement Works

Standard web speech applications apply aggressive DSP filtering—including noise cancellation, echo suppression, and automatic gain control (AGC)—which artificially amplifies quiet whispers and suppresses loud background sounds.

This decibel meter explicitly requests raw unadulterated audio streams:

navigator.mediaDevices.getUserMedia({
  audio: {
    echoCancellation: false,
    noiseSuppression: false,
    autoGainControl: false,
    channelCount: 1,
  },
});

This ensures true physical acoustic dynamics are measured without artificial automatic gain distortion.

IEC 61672-1 Exponential Ballistics

Acoustic waveforms fluctuate thousands of times per second. To create readable, meaningful meter movements, international standards define exponential time constants:

  • Fast ($\tau = 125\text{ ms}$): Follows the rapid rise and fall of vocal consonants and transient impacts.
  • Slow ($\tau = 1000\text{ ms}$): Smoothes momentary spikes to report representative ambient noise levels.

$$y_k = y_{k-1} + (1 - e^{-\Delta t / \tau}) \cdot (x_k - y_{k-1})$$

OSHA & NIOSH Hearing Safety Guidelines

Prolonged exposure to sounds at or above $85\text{ dBSPL}$ causes irreversible damage to the sensitive hair cells (stereocilia) of the cochlea:

Sound Level Common Example Permissible Daily Exposure
$30\text{ dB}$ Quiet bedroom, ticking watch Unlimited
$50\text{ dB}$ Quiet home, gentle rainfall Unlimited
$60 – 65\text{ dB}$ Normal conversational speech Unlimited
$75\text{ dB}$ Busy restaurant, dishwasher Safe
$85\text{ dB}$ Food blender, heavy street traffic 8 hours max per day (OSHA)
$91\text{ dB}$ Lawn mower, subway platform 2 hours max per day
$100\text{ dB}$ Motorcycle, sporting event 15 minutes max without protection
$110+\text{ dB}$ Rock concert, siren, power tools Immediate risk of permanent damage

Use this tool to audit your workspace or living environment and preserve your hearing longevity.

Frequently asked questions

What is the difference between dBFS and dBSPL?

dBFS (Decibels relative to Full Scale) is a purely digital metric where 0 dBFS represents the maximum possible amplitude of digital audio before clipping occurs (always expressed as negative numbers like -20 dBFS). dBSPL (Sound Pressure Level) is a physical acoustic measurement of air pressure waves relative to the threshold of human hearing (20 micropascals, where 0 dBSPL is near silence, normal speech is 60–65 dBSPL, and 120 dBSPL is the threshold of pain).

Why does this browser sound meter need calibration?

Web browsers receive digitized audio numbers from your operating system, but they cannot inherently know the physical microphone hardware sensitivity or preamp gain of your laptop, smartphone, or USB interface. The calibration slider allows you to calibrate against a physical sound meter or standard conversational level (~60–65 dBSPL).

What is the difference between Fast (125ms) and Slow (1000ms) ballistics?

Defined by international sound level meter standards (IEC 61672-1), Fast mode uses a 125ms time constant that reacts rapidly to speech pauses and transient noises, ideal for evaluating peak conversational peaks. Slow mode uses a 1000ms (1 second) time constant to average out short-term fluctuations, ideal for measuring sustained background HVAC noise or traffic levels.

Is my microphone audio private?

Yes, 100%. Web Audio API processes all audio stream buffers locally within your browser's execution memory. No audio stream is ever recorded, stored on disk, or uploaded to any remote server.

Can I use this as an online decibel meter on my iPhone?

Yes, open the page in Safari, grant microphone access, and watch live levels with Fast or Slow ballistics and peak hold. Readings are relative dBFS from an uncalibrated phone microphone, so treat them as comparisons between rooms and moments rather than certified SPL values for legal or safety decisions.

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