How to measure decibels on iPhone

Before we built Loudmark, we read a lot of reviews of other decibel apps. The same few complaints came up again and again. Free apps showed one big number with no idea what it meant. Some showed unweighted dBZ and called it dB, so a quiet fridge looked alarming. Others locked the meter behind a paywall on the first screen. And almost nobody offered a way to check whether the number was even close to right. So we wanted to write the guide we wished those people had found first.

Here is what your iPhone can already do, how to get a reading you can trust a bit more, and where an app fits in.

What your iPhone and Apple Watch can do on their own

Apple has a few hearing features built in, but they are easy to mix up.

The Hearing tile in Control Center. You can add Hearing to Control Center in Settings. When headphones are connected and audio is playing, the tile shows how loud that audio is, with a green or yellow level. It is useful for checking your music volume. It does not measure the room around you.

The Noise app on Apple Watch. If you have an Apple Watch, the Noise app uses the watch mic to measure the sound around you in A-weighted decibels (dBA). It can notify you when the level stays high for a while, and your history shows up under Hearing in the Health app on your iPhone. It is a good everyday check. It is less handy if you want a graph, a calibration offset or something you can share.

A sound meter app. For room noise on the iPhone itself, you need an app that reads the microphone and shows a level. There are many free ones. The quality varies a lot, so the tips below matter more than which app you pick.

How to take a steadier reading

A phone reading is only as good as the way you take it. These steps make the biggest difference.

1. Pick the right weighting. Set the meter to dBA for most jobs. It follows how our ears hear everyday sound. If the app only says “dB” with no letter, it may be unweighted (dBZ), which often reads higher because it counts low rumble you barely hear. Our guide to dBA vs dBC vs dBZ explains the difference.

2. Find the mic. The main mic on most iPhones is on the bottom edge, near the charging port. Point that end toward the sound.

3. Don’t cover the mic. A finger, a pocket or a thick case over the bottom edge can lower the reading by several decibels. Hold the phone by its sides.

4. Keep the distance steady. Sound drops quickly as you move away. As a rough rule, doubling your distance from a single source in open space lowers the level by about 6 dB. Pick a spot, note it, and use the same spot next time.

5. Hold still and stay quiet. Rustling, talking and tapping the screen all count. Set the phone down on a soft surface if you can, or hold it at arm’s length.

6. Measure for at least 30 seconds. The live number jumps around. What you usually want is the average over time, called Leq (equivalent continuous level). Thirty seconds is a sensible minimum. For something that comes and goes, like traffic, a few minutes is better.

7. Note the max and the time. The maximum tells you how loud the peaks got. Write down the date and time with each reading, especially if you are keeping a record.

Fast or slow response

Most meters offer two response speeds.

• Fast updates every 1/8 of a second. It catches short bangs, door slams and claps.
• Slow averages over about 1 second. It gives a calmer number that is easier to read for steady noise like a fan or traffic.

If you are trying to describe “how loud is it in here”, slow plus a 30-second Leq is a good habit. If you want to know how loud the peaks are, use fast and look at the max.

dBA or dBC for your situation

Here is a quick way to choose:

• Room noise, neighbors, offices, traffic: dBA.
• Hearing risk and workplace guidance: dBA, because that is what NIOSH and OSHA use.
• Bass-heavy music or a subwoofer through the wall: check dBC as well. A big gap between dBC and dBA usually means a lot of low-frequency sound.

If you are not sure, take both and write both down.

The limits of an iPhone mic

Phone mics are made for voices, not for measuring loud sound. Two limits are worth knowing.

The top end. iPhone mics typically top out somewhere around 95 to 100 dB. Above that, the reading can flatten out even if the real sound keeps getting louder. If your app shows a number near that ceiling, treat it as “at least this loud”.

The very low and very high end. Phone mics are less sensitive to very deep bass and to very high pitches, so dBC and dBZ readings of bass-heavy sound may come out lower than a real meter would show.

Cases, dust in the mic hole, and the model of iPhone also change things. None of this makes a phone useless. It just means you should compare readings taken the same way, and avoid treating one number as exact.

How to calibrate against a real meter

Calibration does not make a phone into a lab instrument. It does make your readings line up better with one.

1. Borrow a real sound level meter. Some libraries, schools and hire shops lend them. A friend who works in audio may have one.
2. Remove the case and keep it off whenever you measure.
3. Play a steady sound. Pink noise or a fan works better than speech or music.
4. Hold both side by side, same distance, same direction, mics close together.
5. Read both in dBA, slow response, for 30 seconds.
6. Set the offset in your app so the iPhone matches the meter. If the meter says 68 and the phone says 65, add 3 dB.
7. Check one more level if you can, a little quieter or louder, to make sure the offset holds.

Redo it if you change phones or cases.

What to do with the number

A reading on its own is just a number. Two simple ways to make it useful:

• Compare it to everyday sounds. Normal conversation is around 60 dBA. A vacuum cleaner is around 70. Our decibel chart with everyday sounds has more examples and the public guidance on how long is too long.
• Keep a record. If noise from next door is a problem, readings with dates and times are more useful than memory. See how to record noise from neighbors as evidence.

If you are worried about your hearing, such as ringing in the ears or sounds seeming muffled after loud events, please talk to a doctor or an audiologist.

Where Loudmark helps

Loudmark is our decibel meter for iPhone. It is on the App Store and needs iOS 26. We built it around the problems above.

• A live dBA meter, with dBC and dBZ available, and fast or slow response.
• Min, average (Leq) and max for each session, with a scrolling graph so you can see the peaks.
• A plain comparison line, like “As loud as a vacuum cleaner”, so the number means something.
• Calibration of plus or minus 20 dB in 0.5 dB steps, to match a real sound level meter.
• A “near the mic limit” note when the reading gets close to what an iPhone mic can handle.

All of that is free, along with one 85 dB alert and widgets. Loudmark Pro adds an evidence camera, overnight recording, PDF noise reports, a custom alert level, saved reference sounds and a Live Activity. Pro is $24.99 a year with a 3-day free trial, $3.99 a week, or $34.99 once.

There is no account. Sound is only saved when you start a recording, and it stays on your iPhone. Loudmark is not a certified Class 1 or Class 2 sound level meter, so it is best for everyday checks and personal records, not formal measurements.