Your phone already has a microphone. Might as well put it to work.
A sound level meter app uses your device's built in microphone to estimate how loud your environment is. Instead of carrying a dedicated SPL meter around, you open an app and get an immediate reading of the sound pressure level around you, measured in decibels.
The concept has been around for a while, but most sound meter apps treat the experience like an afterthought. You get a number on a screen, maybe a bar graph, and that's it. There's no thought given to how the information is displayed or whether you'd actually want to look at it for more than three seconds.
Decibels takes a different approach. It turns your iPhone or iPad into a sound level meter with a vintage VU meter display that makes readings genuinely pleasant to watch. The app uses your device's microphone to perform RMS (Root Mean Square) analysis of incoming audio, then displays estimated sound pressure levels on a beautifully rendered analog meter face with smooth needle ballistics. It covers a range of 30 to 120 dB SPL, which spans everything from a quiet room to a very loud concert.
It's free. No ads, no subscriptions, no in app purchases. Just a sound meter that works and looks good doing it.
The process is about as straightforward as it gets. Open the app, and it starts listening.
Your iPhone or iPad has a surprisingly capable microphone built into it. Decibels accesses that microphone and continuously samples the ambient sound in your environment. The raw audio signal is processed using RMS analysis, which calculates the effective average power of the sound wave. This is the same fundamental approach that professional audio equipment uses to measure sound intensity.
The result is an estimated sound pressure level, displayed in decibels (dB SPL). That reading appears on the vintage VU meter face, where a physical needle moves with carefully tuned ballistics. Fast attack for sudden sounds, slower decay for the falloff. It behaves the way a real analog meter would, which makes it intuitive to read at a glance.
Below the meter, a digital readout shows the precise numeric value. And in the background, the app is charting your sound levels over time on a live graph, so you can see trends and patterns rather than just a snapshot of the current moment.
The app works in all orientations and adapts its layout automatically to whatever device and position you're using. Portrait on an iPhone for quick checks, landscape on an iPad for extended monitoring sessions. The interface adjusts to give you the best view of the meter and chart regardless of how you're holding the device.
Decibels covers a measurement range of 30 to 120 dB SPL, which is where virtually all everyday sound happens.
At the low end, 30 dB is roughly the level of a quiet whisper or a very still room at night. This is about as quiet as most environments get unless you're in a recording studio or anechoic chamber. At the high end, 120 dB is the threshold of pain and roughly equivalent to standing next to a speaker at a loud concert. You really don't want to be there without hearing protection.
In between, you've got normal conversation at around 60 dB, a vacuum cleaner at 70 dB, a busy restaurant at about 80 dB, and a lawn mower at 90 dB. The 30 to 120 dB range captures every sound you'd realistically want to measure in daily life.
One thing to keep in mind: the readings from any phone based sound meter are estimates. Your iPhone's microphone is designed for phone calls and voice memos, not laboratory grade acoustic measurement. Decibels does its best to provide useful readings, and for general reference purposes it works very well. But if you need certified measurements for workplace safety compliance or scientific research, you need a calibrated professional instrument.
Readings from Decibels are estimates for general reference and should not be used for scientific or safety critical applications.
Sound meter apps tend to cram in features nobody asked for. Decibels focuses on the ones you'll actually use.
Vintage VU meter display. This is the centerpiece. The meter face is modeled after classic analog VU meters from the golden age of audio equipment. Cream colored background, precise scale markings, a needle that moves with authentic ballistics. It's not just decorative. Analog meter movement is genuinely easier to read than a bouncing number because your brain processes the needle position and movement speed simultaneously. You get an intuitive sense of loudness that a digital readout alone can't provide.
Live charting. Below the meter, a scrolling chart plots your sound levels over time. This is invaluable when you're trying to understand patterns rather than just instantaneous levels. Is your office consistently noisy, or does it spike when the HVAC kicks on? Is the traffic noise at your apartment worse at certain times? The chart shows trends that a single number reading would miss entirely.
Peak detection. The app automatically tracks and displays the highest sound level it has recorded during your session. This matters because peaks are often the most relevant data point. You might be monitoring a generally quiet environment but want to know how loud that occasional siren or door slam actually gets.
Adaptive layout. Decibels works on both iPhone and iPad, in portrait and landscape orientation. The interface rearranges itself intelligently to make the best use of whatever screen real estate is available. On an iPad in landscape, you get a generous view of both the meter and the chart side by side. On an iPhone in portrait, the layout prioritizes the meter with the chart below.
More people than you might expect. Once you can measure sound, you start noticing it everywhere.
Home studio folks. If you're recording music, podcasts, or voiceover at home, ambient noise is your enemy. A sound level meter app gives you a quick read on how quiet your recording space actually is. Is your room sitting at 35 dB or 50 dB? That difference matters enormously when you're trying to capture clean audio. Decibels won't replace a studio grade measurement system, but it gives you a useful baseline reference before you hit record.
Content creators. Scouting a venue for a shoot? Trying to figure out if a coffee shop is too noisy for an interview? A quick sound check with Decibels tells you what you need to know in seconds. The live charting is especially useful here because it shows you whether the noise is consistent or comes in unpredictable bursts.
Office workers. Open plan offices are notoriously noisy, and noise levels directly affect productivity. If you're trying to make a case for better acoustic treatment or a quieter workspace, having actual data (even estimated data) is more persuasive than saying "it's loud in here." Monitor with Decibels over a few hours and show the chart to your facilities team.
Travelers. Hotel room facing the highway? Airbnb next to a construction site? A sound level meter app helps you evaluate whether a space is going to be livable before you commit. It's also useful for comparing different rooms or floors if the hotel offers to move you.
Curious people. Sometimes you just want to know how loud something is. How loud is your dishwasher? Your neighbor's dog? The subway platform? Sound is invisible, and having a way to quantify it is genuinely interesting once you start paying attention.
Download Decibels from the App Store, open it, and you're measuring sound. That's the whole tutorial.
The app will ask for microphone access when you first launch it. Say yes. Without microphone access, a sound level meter is just a picture of a meter. Once you grant permission, Decibels starts listening immediately and the VU meter needle begins responding to your environment.
For the most useful readings, hold your phone at arm's length away from your body. Sound reflects off surfaces (including you), so a little distance helps the microphone get a cleaner sample. Don't cover the microphone with your hand or a case that blocks the mic opening. And try to keep the device relatively still, since moving it quickly through the air can create wind noise that affects the reading.
Beyond that, just watch the meter. The VU needle gives you an immediate, intuitive sense of the sound level. The chart below shows you how things change over time. And the peak indicator catches the loudest moments so you don't have to stare at the screen constantly.
Decibels is free with no strings attached. No ads, no premium tier, no subscriptions. You get the full app, every feature, for nothing.
A sound level meter that's actually nice to look at. Free on the App Store.
