How do I measure how loud something is with my phone?
Decibel Pro: dB Sound Meter reads the iPhone microphone and shows the level in dBA as it happens, holding minimum, average and maximum on screen. Colour tells you where you are, with anything past 90 dBA in the red. No audio is saved.
How it works
- Allow the microphone
iOS asks once, on the first measurement. The permission is what lets the app read sound level at all, and denying it leaves the gauge sitting at zero rather than failing loudly.
- Hold the phone properly
Keep your hand clear of the microphone at the bottom edge, hold the phone out away from your body rather than against it, and put it at roughly the height of whatever you are measuring.
- Start the scan and let it settle
The gauge tracks the room live while minimum, average and maximum accumulate underneath. A single instant tells you very little, so give it thirty seconds or more before treating the average as the answer.
- Stop, and read the numbers that held
Stopping saves the run as a session with its minimum, average, maximum, duration, the weighting used and any calibration offset applied. That record, not the peak you happened to catch, is what to quote.
The app
- Price
- Free to download with three free scans. The fourth scan, the frequency spectrum tab, the noise dose tab and CSV or PDF export are a paid unlock.
- Requires
- iPhone, iOS 17.0 or later. Microphone permission, which iOS asks for on first use.
- Account
- None. No sign-up, and no audio is ever recorded, stored or sent. Only the numbers are kept.
- Publisher
- Cloud Motion Lab LLC
Common questions
How accurate is a phone compared to a real sound meter?
Close enough to make a decision, not close enough to make a case. A phone microphone is tuned for speech, applies its own gain control, and flattens out well before a jet engine does, so readings at the extremes drift. In ordinary rooms, between about 50 and 90 dBA, a calibrated phone lands within a few decibels of a hand meter. Decibel Pro carries a trim of plus or minus 20 dB so you can match one.
At what point does noise actually damage hearing?
Two published standards disagree slightly and the app implements both. NIOSH sets its recommended limit at 85 dBA averaged over eight hours, halving the safe time for every 3 dB above that. OSHA's legal ceiling is 90 dBA with a 5 dB exchange rate, which is the more permissive of the two. Under the NIOSH rule, 100 dBA, roughly a nightclub, uses up a full day's allowance in about fifteen minutes.
What does the A in dBA mean?
It is a filter applied before the number is calculated. A-weighting discounts the very low and very high frequencies your ear is poor at hearing, which is why it is the weighting written into hearing regulations. C-weighting keeps the bass and is what live sound engineers use for peak levels. Z is flat and unweighted, for calibration. All three are selectable, and the display label changes with them.
Is Decibel Pro free?
Three scans are free and complete, with the live gauge, the waveform and the statistics all working. The fourth scan asks you to pay. The frequency spectrum tab and the noise dose tab, which tracks cumulative exposure against NIOSH or OSHA across a day, are behind the same purchase.
Support
dev@slyapp.coIf a number looks wrong for the room you are standing in, that is usually calibration rather than a bug, and we can talk you through the trim. Send the reading you saw and what you were measuring.