Hardware
TesterSound Level Meter
Free online sound level meter: measure relative dB with your mic, log min/max/average, calibrate against a reference, and export a timestamped CSV.
Have feedback? Report bugs, suggest features, or share your thoughts — we read them allAbout Sound Level Meter
Measure environmental noise and sound levels with a professional decibel meter. Monitor ambient noise in real-time using your device's microphone, track maximum and average dB levels, and receive warnings when noise reaches potentially harmful levels. Perfect for measuring workplace noise, testing acoustic environments, or monitoring sound pollution.
- Press Start measuring to activate your microphone and begin measuring relative sound levels.
- Optionally set a calibration offset (dB) to zero or match the reading against a known reference SPL source.
- Watch the analog meter needle move as sound levels change; the number shown is an instantaneous smoothed relative reading, not LAeq.
- Monitor the time-based history chart and the live minimum, maximum, and average statistics.
- If sound exceeds 85 dB on the display scale, you'll see a "Too loud!" warning indicating potential hearing risk.
- Press Stop, then Export CSV to download a timestamped log of the session to attach to a report or compare devices.
- Use the reference guide to interpret the relative levels, and Reset to clear all statistics between sessions.
Frequently Asked Questions
No. This web tool reads the microphone's normalized time-domain signal (samples in the −1…+1 range), computes the RMS amplitude, and converts it to a relative dBFS value that is then mapped onto a 0–120 display scale. That displayed number is a RELATIVE, uncalibrated reading — it is not certified sound pressure level referenced to 20 μPa, because the browser never exposes the absolute acoustic pressure or the microphone's sensitivity. To calibrate, place your device next to a trusted reference meter (a Type 2 SPL meter, or a calibrated app such as NIOSH SLM) measuring the same steady source, then enter the difference in the Calibration offset (dB) field so this tool's reading matches the reference. After that the relative trend, min/max/average, and exported CSV are useful for comparing devices and logging changes, even though the absolute value remains an estimate.
No. All processing happens locally in your browser using the Web Audio API. The microphone stream is analyzed in real time to compute amplitude values; the raw audio is never stored, never written to a file, and never sent to any server. The only thing you can save is the Export CSV file, which contains just two columns — elapsed time in seconds and the relative dB value at each 100 ms sample — generated entirely on your device. When you press Stop the audio context is closed and every microphone track is stopped, so the browser's recording indicator turns off. Nothing leaves your machine.
It works in any browser that implements getUserMedia and the Web Audio API over a secure (HTTPS) origin: desktop Chrome, Edge, Firefox, Safari, and Opera, plus Android Chrome/Firefox and iOS Safari 14.5+. A few caveats: the page must be served over HTTPS (or localhost) or the microphone API is unavailable and the tool shows an HTTPS-required message. iOS Safari requires the audio context to be resumed inside a user gesture, which this tool does on the Start button, and only one tab may hold the mic at a time. If permission was previously denied, the tool detects that via the Permissions API and shows a blocked state before you click Start. On unsupported browsers it shows an honest not-supported message rather than faking a reading.
A sound level meter measures the sound pressure level (SPL) in your environment in decibels (dB). SPL is a logarithmic ratio of measured pressure to a reference pressure of 20 micropascals (the threshold of human hearing at 1 kHz). The microphone converts air-pressure variations into a voltage, the app squares and time-averages that signal, then converts to dB via 20 × log₁₀(p/p_ref). Phones typically report dB SPL with A-weighting (dBA), a frequency-response curve that mirrors human ear sensitivity and de-emphasizes very low and very high frequencies. C-weighting (dBC) is used for measuring peak impulse noise. The display range usually covers 30–120 dB, with anything above 85 dB considered hearing-damaging over time.
Phone microphones vary widely in calibration — two phones at the same desk can report numbers 10 dB apart for identical noise. Testing against a known reference (a friend playing a steady 1 kHz tone at a fixed volume, or a calibrated SPL meter app like NIOSH SLM) shows how trustworthy your phone is for occupational hearing safety, traffic noise complaints, or home theater tuning. Modern iPhones (post iPhone 7) and Pixels actually use multiple mics and software processing that has been independently validated to within ±2 dBA of professional meters, but older or third-party Android phones can drift 10–15 dBA. This tester also helps identify mic dust, broken aux ports, or buggy automatic gain control.
The standard unit is decibels of sound pressure level (dB SPL), referenced to 20 μPa. Variants include dBA (A-weighted, the most common for environmental noise), dBC (C-weighted, for peak impulses), and dBZ (unweighted, flat). Time-weighting matters too: 'Fast' uses a 125 ms integration window, 'Slow' uses 1 second, and 'Peak' captures instantaneous spikes. The numeric scale ranges from 0 dB (hearing threshold) to 120 dB (jet engine at 30 m), with 60 dB conversation, 85 dB heavy traffic, 100 dB chainsaw. Doubling the sound energy adds 3 dB; doubling perceived loudness adds about 10 dB. Hearing damage thresholds: 8 hours at 85 dBA is the OSHA limit; 1 hour at 94 dBA; 15 minutes at 100 dBA.
Smartphone microphones are highly directional, especially at high frequencies. Pointing the mic away from a noise source can drop the reading by 5–10 dB, while pointing the mic at a hard wall produces reflections that add 3–6 dB. Pocket noise (clothing rubbing the mic), wind noise (gusts hitting the port), and handling noise (touching the phone) all add 10–20 dB of artifact. Even breath from the user reading the screen can spike low frequencies. For consistent measurements, hold the phone at arm's length, point the bottom mic toward the source, avoid windy conditions, and let the reading stabilize for 5–10 seconds. The 'Slow' time-weighting setting smooths these short-term variations into a meaningful average.
A-weighting is a frequency-response filter that mimics human hearing sensitivity, attenuating frequencies below 1 kHz and above 6 kHz where our ears are less sensitive. The IEC 61672 standard defines the exact A-curve, derived from the inverse of the 40-phon equal-loudness contour. Almost all environmental noise regulations (OSHA, NIOSH, EU Environmental Noise Directive) and product noise specs (refrigerators, cars) use dBA because it correlates with perceived loudness and risk of hearing damage. Use C-weighting only for impulsive noise (gunshots, fireworks, machinery slams) where low frequencies matter, or Z-weighting for scientific frequency analysis. A meter reporting dBA on a low-frequency rumble may read much lower than dBC for the same physical pressure.
Yes, with caveats. A 2014 NIOSH study compared 130 smartphone SLM apps to a Type 1 reference meter and found iOS apps using the calibrated NIOSH SLM averaged within ±2 dBA across the 65–95 dBA range — comparable to a Type 2 (general-purpose) meter under ANSI S1.4. Android performance was wider due to MEMS mic variation across manufacturers. Modern phones use MEMS digital microphones (Knowles SPH0645, ST IMP34DT05) with -38 dBV/Pa sensitivity and 64 dB SNR, more than adequate for typical noise levels. Limitations: phone mics saturate above ~120 dB SPL (loud concerts), have rolling AGC that distorts steady readings, and lack the calibrated diffuse-field correction of a true Type 1 meter.
The Web Audio API combined with getUserMedia is used. After requesting microphone permission via navigator.mediaDevices.getUserMedia({audio: true}), the audio stream feeds into an AnalyserNode that returns time-domain or frequency-domain data at 44.1 or 48 kHz sample rate. JavaScript computes the RMS amplitude per analysis frame, applies an A-weighting filter (cascaded biquads), then converts to dB. For mobile compatibility, audio context must be resumed inside a user-gesture handler; iOS Safari requires explicit user interaction. The Permissions API tracks consent state. Note that browsers expose normalized audio values (-1 to +1), not calibrated voltage, so absolute dB SPL requires an external calibration step against a known sound source.
IEC 61672 (also published as ANSI S1.4) is the master standard, defining three meter classes: Type 1 (precision, ±0.7 dB tolerance) used for legal and scientific work, Type 2 (general purpose, ±1.5 dB) used by industrial hygienists, and Type 3 (survey, deprecated). The A-, C-, and Z-frequency weightings are specified in this standard. OSHA 1910.95 sets workplace permissible exposure limits (90 dBA TWA, 85 dBA action level), while NIOSH recommends 85 dBA TWA. The WHO's 2018 Environmental Noise Guidelines target ≤45 dB Lnight for residential sleep protection. Phone apps cannot legally claim Type 1 or Type 2 compliance without calibration documentation, but the NIOSH SLM iOS app comes closest, validated to ±2 dBA across the 65–95 dBA range against a B&K Type 1 reference.
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