Getting started with dB Toolkit
Take your first measurement in a minute, understand what the numbers mean, and learn how to keep a record you can hand to someone else.
What dB Toolkit is
dB Toolkit is a sound level meter for iPhone built to keep a record of noise, not just show a number. The live meter - calibrated dBA, dBC and dBZ with the statistics and a history graph - is free. A one-time Pro unlock adds recording sessions, saved history, PDF and CSV reports, measuring against published limits and the analysis tools.
It is a phone, not a Class 1 or Class 2 sound level meter, and it says so. What it gives you is a competent, timestamped record with its uncertainty stated.
Your first reading in a minute
- Open the app, tap through the four intro panes (or Skip) and allow the microphone.
- The meter is already running: the dot beside "dB Toolkit" is green and the big number is the current level in dBA.
- Point the top of the phone (the camera end) at what you are measuring, at arm's length, with nothing covering the microphone.
- Read the dial, the "LIVE 30s" graph below it and the five statistics under the graph.
- Tap the A, C or Z chips to change the frequency weighting, and Reset to clear the peak marker and the graph.
What the numbers mean
- LAeq is the energy average: the steady level that carries the same total energy as the whole measurement.
- LA10 is the level exceeded 10% of the time, so it describes the louder events.
- LA50 is the level exceeded half the time, the median.
- LA90 is the level exceeded 90% of the time: the background noise floor, which assessments such as BS 4142 compare against.
- LAmax is the highest time-weighted level reached.
Tap any statistic box for a plain-English explanation. dBA follows human hearing and is what most regulations use; dBC keeps the low end and is used for peak limits and rumble; dBZ applies no weighting. Fast, Slow and Impulse time weighting are in Settings under Measurement.
Measuring so the reading means something
- Hold the top of the phone towards the source. The calibration was derived through that microphone.
- A hand or a case over the microphone, or the phone held against your chest, reads low by several decibels.
- Moving a metre in a room can change the level by several decibels, so measure where the problem is.
- Very loud sounds, much above about 100 dB, make a phone microphone clip, and a clipped reading under-reads.
- Measure the background as well: most assessments are about the difference between a sound and the quiet it sits in.
Calibration
There is nothing to do. iPhones publish no microphone sensitivity, so the app ships a constant measured against a calibrated reference microphone and applies it automatically. Settings, under Calibration, tells you which of four states your scale is in: measured for this device, estimated from this generation, estimated for a typical iPhone, or not calibrated. The stated uncertainty is printed on every report - about five decibels on the iPhone that was measured and six or seven on other models.
You can add your own manual offset, and with Pro you can measure through a calibrated USB measurement microphone, but neither is required.
Keeping a record (Pro)
- Tap Record. After a countdown (10 seconds by default) the session starts, and it keeps measuring with the screen locked.
- A recording stops after 5 minutes unless you change Duration in Settings under Timing; you can set it up to 60 minutes, or to Manual for no limit.
- Tap Stop Recording, then Save (or Discard). You can add a short description of where you measured.
- Open History for your saved sessions: the statistics, the level graph with the audio waveform on one time axis, and trim handles that the statistics follow.
- Share a one-page PDF report or the CSV data from the session screen.
A report carries the date and duration, the weighting, the calibration state and its uncertainty, the statistics, the peak events, any gap or interruption stated above the statistics and, if you chose a published limit, a pass, fail or too-close-to-call verdict with its source named. The app keeps your 50 most recent saved sessions.
Analyser, generator and room measurement (Pro)
The Analyser shows the spectrum (and a spectrogram) in narrowband, octave and third-octave views and names the loudest tone and its nearest musical note. The Generator plays tones, white, pink and brown noise and sweeps, and warns that the meter can hear it. Room measurement plays a sweep and returns reverberation time per octave band. Free users see these dimmed with a Pro badge.
Free and Pro
The live meter is free and stays free: dBA, dBC and dBZ, Fast, Slow and Impulse, the calibrated scale with its uncertainty, the live statistics, the history graph and peak markers. Pro is a single one-time payment, with no subscription and no ads, that unlocks recording, saved sessions, reports and export, limits and noise dose, the analyser, the generator, room measurement and measurement-microphone support. Use Restore purchase on the Pro screen if you reinstall.
Privacy
There is no account, no analytics, no advertising and no server. Audio is saved only when you record a session, stays on your phone and is deleted with the session. The one location fix is taken at the start of a recording and is optional. Measuring needs no internet connection; only buying or restoring Pro uses the App Store.
Questions people ask
Do I need to calibrate it?
No. It ships with a constant measured on an iPhone 16 and applies it automatically, and every report states whether your scale is measured or estimated and its uncertainty. A manual offset is optional.
How accurate is it?
It is a phone, not a certified meter. Comparisons and differences within one measurement are more reliable than a single absolute figure, and where you hold the phone can matter by several decibels.
Will a report stand up in court or with my council?
The app does not claim that. It gives you a dated record with its calibration and uncertainty stated. For a formal enforcement action or court you need a calibrated instrument and somebody qualified to use it.
What is free and what needs Pro?
The live meter, weightings, calibration, live statistics and history graph are free. Recording, saved history, PDF and CSV export, limits and dose, the analyser, the generator and room measurement are part of the one-time Pro unlock.
Does it record audio, and is anything uploaded?
Audio is saved only when you record a session, on your phone, and is deleted with the session. The app has no server and does not upload anything; you choose what to share.
Can it run overnight with the screen locked?
Yes. A recording continues with the screen locked or in another app. Set Duration to Manual first, because the default stops at 5 minutes, and remember the app keeps 50 saved sessions.
Can I use an external microphone?
With Pro, a calibrated USB measurement microphone can be used. Calibration files from Dayton Audio import directly; for others you type the sensitivity from the file for your unit. The app flags in amber an attached microphone it has no sensitivity for.