Your phone can already hear. Here's how to make it listen.
Short answer: yes, to a reasonable degree. Your iPhone has a surprisingly good microphone, and with the right app, it can give you useful decibel readings.
Every iPhone has at least three microphones built into it. These mics are designed to capture voice for phone calls, FaceTime, Siri, and video recording. They're not calibrated acoustic measurement instruments, but they're sensitive, well engineered pieces of hardware that can detect a wide range of sound levels.
When a sound level meter app like Decibels accesses your iPhone's microphone, it captures the raw audio signal and processes it using RMS (Root Mean Square) analysis. This calculates the effective power of the sound wave and converts it to an estimated decibel reading. The result is a sound pressure level (SPL) estimate that gives you a genuine sense of how loud your environment is. Decibels applies A-weighting (dBA), or leaves the signal unweighted, following the curves IEC 61672 specifies, with Fast and Slow time weighting to choose from.
Is it as accurate as a professional sound level meter? No. Professional meters use calibrated microphones with known frequency response curves, and they conform to standards like IEC 61672. Your iPhone microphone has a frequency response optimized for human voice, not flat spectrum measurement. The readings will vary somewhat from device to device and won't perfectly match a calibrated instrument.
But for practical, everyday purposes? It's remarkably useful. If you want to know whether your office is at 50 dB or 75 dB, whether your neighbor's party is truly unreasonable, or whether your kid's drum practice is approaching the range where you should worry about hearing, an iPhone sound level meter gives you that information quickly and for free.
The whole process takes about ten seconds. Seriously.
Step 1: Download Decibels. It's free on the App Store. No account needed, no signup, no trial period. You download it and it works.
Step 2: Open the app. When you launch Decibels for the first time, it will ask for permission to access your microphone. Grant it. Without microphone access, a sound meter app can't do much.
Step 3: Press start. The vintage VU meter needle begins moving, responding to the sound in your environment. The digital readout below shows the current level, with the running average (Leq), the maximum and the minimum beneath it and the elapsed time alongside. A trace at the bottom plots the last ten seconds.
Step 4: Press stop — and that's the whole thing. The run saves itself the moment you stop it: average, maximum, minimum, LCpeak, duration and the complete level trace, filed under the day and time it was taken. There is no Save button to remember, and nothing to name.
There are no settings you must configure first and no calibration wizard to suffer through. If you want to check a noise level, you hold up your phone, press start, and look at the screen. The one setting worth finding later is the calibration offset, which lets you line the app up against a reference meter if you ever have one to hand.
The VU meter shows your real-time reading with authentic analog needle movement. The trace at the bottom shows the last ten seconds on a fixed timeline, so a sudden bang draws as a spike rather than flattening out at the top of the scale. The maximum holds the loudest moment, and LCpeak — the true C-weighted peak, untimed — catches the short, hard sounds that a time-weighted maximum tends to under-report.
The app does the hard work, but a few simple habits will improve the accuracy of your measurements.
Hold your phone at arm's length. Sound reflects off your body, clothes, and anything else near the microphone. Holding the phone away from you reduces these reflections and gives the mic a cleaner sample of the ambient sound. Think of it like pointing a camera at something. You want the microphone aimed at the sound source, not buried in your lap.
Don't cover the microphone. This sounds obvious, but it's the most common mistake. Your iPhone's primary microphone is on the bottom edge (for most models). If you're gripping the phone in a way that blocks or cups over that area, your readings will be lower than the actual sound level. A phone case that covers the microphone opening will also muffle the readings. If your case has a thick border around the bottom edge, consider removing it for measurements.
Minimize vibration and handling noise. Moving the phone quickly through the air creates wind noise. Tapping, rubbing, or adjusting your grip generates handling noise that the microphone picks up. For the most accurate reading, hold the phone steady and avoid fidgeting with it during the measurement. If you need extended monitoring, setting the phone on a stable surface works well.
Be aware of reflective surfaces. Sound bounces off walls, floors, ceilings, and hard furniture. If you're standing in a corner, the reflected sound will make the reading higher than it would be in the middle of the room. For the most representative measurement, try to position yourself where you'd normally be in that space.
Give it a few seconds — or better, let it run. Sound levels fluctuate constantly, and a single glance at the meter might catch a peak or a trough. Watch it for at least 15 to 30 seconds to get a sense of the typical level. Better still, let the measurement run and read the average (Leq) rather than the needle: that is the number that actually characterizes a period of time. The live trace covers the last ten seconds, but the full shape of the run is kept in the saved measurement, so a long one costs you nothing but patience.
Close other apps that use the microphone. If another app is actively using the microphone (like a voice recorder or a phone call), it may interfere with Decibels' access to the audio hardware. Close other audio apps before measuring for the cleanest results.
Honesty time. Here's where phone based sound measurement works great, and where it doesn't.
Where it works well. General reference measurements. Comparing relative loudness between environments. Getting a ballpark sense of whether something is at 50 dB or 80 dB. Monitoring trends over time. Satisfying curiosity about everyday noise levels. For all of these purposes, an iPhone with a good sound level meter app is genuinely useful and far better than guessing.
Where it falls short. Certified workplace safety compliance. Scientific acoustic research. Legal noise dispute evidence. Medical hearing assessment. Calibrated environmental monitoring. All of these applications require professional grade instruments with known calibration certificates. Your iPhone is not that instrument, no matter what app you put on it.
The main limitation is calibration. A professional sound level meter has a microphone with a documented, verified frequency response. It's been tested against a known reference and has a certificate saying its readings are accurate within a specified tolerance. Your iPhone's microphone is a mass produced component that varies slightly from unit to unit and was designed to make your voice sound good on phone calls, not to produce scientifically precise measurements.
That said, for the 95% of situations where you just want to know "roughly how loud is this," an iPhone sound level meter is a practical, accessible, and surprisingly capable tool. Just understand what it is and isn't.
Decibels provides estimated readings for general reference. They should not be relied upon for scientific or safety critical applications.
Once you have a sound meter on your phone, you'll find reasons to use it in places you wouldn't expect.
Is your neighbor actually that loud? You think the apartment next door is unreasonably noisy, but is it? Check with Decibels. If the noise is coming through at 55 dB, it's annoying but probably within normal limits. If it's registering at 75 dB inside your apartment, that's a different conversation. And because the run is saved with its date, its duration and its full trace, you end up with something better than a remembered number: a measurement you can export as a CSV and send on, with the weighting and calibration it was taken under attached, so the person reading it knows what they're looking at.
Is your home office quiet enough for calls? Video calls pick up background noise, and what sounds fine to your ears can sound terrible through a mic. If your office ambient noise is above 50 dB, your call participants are probably hearing more background than you think. Measure it, and if it's high, figure out what's contributing. Sometimes it's a fan, an open window, or an appliance you've gotten so used to that you've stopped noticing it.
How loud is your kid's drum kit, really? As a parent, you oscillate between "this is fine" and "everyone in the neighborhood hates us." Measure the drum kit at the property line. If it's under 65 dB outside, your neighbors probably can't hear much. If it's at 85 dB, you might want to invest in some drum mutes or relocate practice time.
Is that restaurant going to work for conversation? You're planning dinner at a spot that looks great online but might be deafeningly loud in person. Pop in, hold up your phone, and check. Anything above 80 dB means you'll be shouting across the table. Below 70 dB and you can actually talk. This takes ten seconds and saves you a frustrating evening.
How loud is your commute? Subway platforms in many cities regularly exceed 90 dB when a train arrives. That's louder than most people realize and well into the range where daily exposure matters. Measuring your commute once can motivate you to start wearing earplugs in the subway, which is one of those small health decisions that compounds over decades.
Does your white noise machine actually help? You bought a white noise machine for the bedroom, but is it actually loud enough to mask the street noise? Measure the street noise, then measure the white noise machine. If the machine is at 50 dB and the noise you're trying to mask is at 55 dB, you might need to turn it up or reposition it.
Decibels isn't just for iPhones. It runs natively on iPad, with an interface that takes advantage of the larger screen.
On an iPad, especially in landscape orientation, the layout splits into two columns: the VU meter on one side, the readings, controls and level trace on the other. This makes the iPad particularly well suited for extended monitoring sessions where you want to watch levels move without squinting at a phone screen.
The app's adaptive layout means it works in any orientation on either device. Portrait or landscape, iPhone or iPad, the interface rearranges itself to make the best use of the available screen space. The meter, the numbers and the trace resize and reposition automatically.
If you're using Decibels for something like monitoring ambient noise in a room over several hours, propping an iPad up on a desk gives you a dashboard you can glance at throughout the day — and when you stop it, the whole run is saved rather than lost. One caveat worth knowing: leaving the app ends the measurement. Decibels doesn't record in the background, so the device needs to stay on the app for the duration.
Turn your iPhone into a sound level meter. Free, forever.
