Acoustic Ruler

Translations available: Esta página en Español, Diese Seite auf Deutsch

Acoustic Ruler Pro has been featured on Cult of Mac, Techcrunch, GIZMODO, lifehacker, and MAKE.

Wouldn’t it be amazing to have a ruler in your pocket all the time? Well now you can! Measure distances of up to 25 meters (82 feet) with Acoustic Ruler Pro for the iPhone, iPod touch, and iPad (App Store Link). Scroll down for the details or watch the two videos showing the two different operation modes first:

This video shows the dual device mode with two iPod touch devices:

This video shows the single device mode with an iPad:

The app works by clocking the time delay of the emitted sound waves. There are two different operation modes: a single device operation (with headphones) and a dual device mode for measuring the distance *between* two devices. Read below to find out which modes work on your iOS device.

Single device (headphone) mode:

This mode works on the iPhone 3GS (and newer), iPod touch 3rd Generation (and newer) and on all iPads. You either need one of those devices and headphones with a mic or headphones without a mic and a iOS device with a built-in mic (excluding the iPod touch 3rd Generation). The resolution in this mode is 1mm or 1/10 of an inch, depending on the unit system you have selected.

Dual device mode:

For this mode you need two compatible iOS devices. These are: iPhone 3GS (and newer), iPod touch 4th Generation and all iPads. One device has to be started as the master device, and the other as the reflector device. The measurement is started on the master device, by pressing the “Measure” button. The reflector device then sends back the chirp of the master which displays the measurement result. The resolution in this mode is 1cm or 1/2 of an inch.

When you first start the program, it will guide you through the easy calibration steps with text and illustrations explaining what to do. Please recalibrate when you are getting wrong measurements.

The app lets you set the air temperature as an additional calibration. This is important, because the speed of sound varies considerably with temperature, affecting the precision of the measurements.

You can switch between displaying the measurement in feet/inches and meters/centimeters. Accordingly, the air temperature will either be set in degrees fahrenheit or celsius.

Please note that while the resolution of the measurements may be as low as 1mm and I have taken great care to make the app as reliable as possible, there are simply too many factors affecting the measurement process and the accuracy. That’s why there is no warranty that the measurements taken with Acoustic Ruler Pro are 100% correct. Since the app works by sending and receiving sound, you’ll obviously get the best results when using it in an environment that is not too loud.

You can install Acoustic Ruler Pro by following this link.

If you have any problems with the app, please leave a message below or via Twitter (preferably before giving the app a negative review). I will do what I can to get the app running perfectly on your device! Customer satisfaction is very important to me.

Follow @acoustic_ruler on Twitter to stay up to date with the newest developments, or to report any problems you may have.

Acoustic Ruler on cheap hardware

I regularly get inquiries from companies and individuals who are interested in acoustic distance measurement. In most cases it is not an option to buy two iPod touch devices. That’s why I’m trying to get my acoustic distance measurement method running on the cheapest possible hardware.

In the video you see my messy desk and the C5535 eZdsp USB Stick Development Kit from Texas Instruments. On the small OLED display, the left number is the measurement in millimeters. I have since abandoned the DSP route because of new plans for making it work on even cheaper hardware.

  1. [...] Acoustic Ruler « iq-tainment: “Measure distances of up to 25 meters (82 feet) with Acoustic Ruler Pro for the iPhone, iPod [...]

  2. Tyler says:

    That is pretty neat. Excellent job!

  3. Sameer Verma says:

    The OLPC XO has had this for a while. See it here in action.

    Code for the application is available at

  4. Ryan says:

    When done between two devices, is the distance measured between the ends of the iDevices? If so, could you add a handy switch that compensates the length of the device? That would make it easy if we put two devices against opposite walls to get the wall-to-wall distance. As two iPhones could subtract about 8″ from the measurement.

    • Thanks for your suggestion! When you measure with two devices the distance is measured between the devices (i.e. if they touch, it’s 0). I have been thinking about your suggestion, and it is actually a bit more complicated, because you would have to select which device the other device is (an iPad is longer)… May be in an update…

      • Ryan says:

        Thanks for the confirmation.

        (I’m a software guy also, so I like tossing out random suggestions without really thinking about how much work it would be ;-) )
        How about in the calibration phase you could have the reflector send back a simple audio sequence that lets the master know what it is? Since it is such a small amount of data with a fixed set of variables you could probably get by reliably with a very low bit rate and no ECC.

  5. Why not measure the reflected path and do away with having to use a microphone?

    • I wanted to do new, and there already was an app on the App Store that tried to do this. I didn’t try it out, but I think it didn’t work very well, because it mostly had negative reviews/ratings.

      • Adam says:

        I bought the reflected path app sound ruler. It works sometimes depending on what it is pointed at. The accuracy wasn’t very good though from what I remember (it was over a year ago that I looked at it).

  6. Chris Rose says:

    I’ve been waiting for such an app for a long time – thanks thanks thanks for doing this!

  7. I love to leverage the features of my device as much as possible, this is a great example.

    Could a complimentary app be made using the iphone’s camera and a visual target ( let’s say a business card sized ‘X’ )?

    just an idea

  8. [...] way to take measurements using sound waves with an iPhone. German developer Florian Student’s Acoustic Ruler Pro for iOS will measure distances up to 25 meters by clocking the time delay of emitted sound waves. [...]

  9. Alan says:

    Hi, fantastic app I really love it. Would the idea of wall to wall measurement be to difficult to do.I use iPhone and iPod of similar lengths simple to add the difference but was just wondering if it could be achieved within the app?
    Looking forward to many uses for this app, many thanks.

  10. [...] Acoustic Ruler | iq-tainment. [...]

  11. Alan says:

    Purchased your acoustic ruler pro, really cool app.
    Was a bit dubious about it’s reliability but was pleasantly
    Surprised at the measurements I have been getting, most
    Have been within a couple of mil, fantastic piece of work.

  12. [...] With Your iPhone Like a Submarine [Video] Antowns — 11/14/2011 07:17 PM — Thanks to a new app that uses the same approach as submarines for measuring distance, you can now add [...]

  13. [...] to a new app that uses the same approach as submarines for measuring distance, you can now add [...]

  14. L’application Acoustic Ruler permet en effet de mesurer des distances jusqu’à 25 mètres en utilisant 2 appareils sous iOS

  15. Acoustical Ruler misst die Laufzeit von Schall und errechnet daraus die zurückgelegte Distanz. Im Zweigeräte-Modus lassen sich so Entfernungen von bis zu 25 Metern ausmessen

  16. iPhone hacks are pretty cool and this is one of the cooler of the cool ones. It’s an app that sends out an acoustic wave in order to measure the distance between two phones or between the phone and a microphone.

  17. iPhone hacks have been flattering cold as well as this is the single of the cooler of the cold ones. It’s an app which sends out an acoustic call in sequence to magnitude the stretch in in between dual phones or in in between the phone as well as the microphone.

  18. IQ-Tainment has a really cool iPhone hack. They have developed and app that emits acoustic waves that measures the distance between two phones or between the phone and a microphone.

  19. No more carrying bulky rulers or yardsticks in your pocket! the Acoustic Ruler is one app to rule them all! The app works by clocking the time delay of the emitted sounds waves.

  20. [...] Sul sito dello sviluppatore trovate maggiori dettagli sull’applicazione. [...]

  21. bokusama says:

    I never carry with me a normal headset. What I always use is a wireless Bluetooth headset which is way more comfortable. Unfortunately this does not seem to be enabled for Bluetooth devices. Is there in a reason for that?

    • There are two reasons for that: a) the delay that is a result of the bluetooth transmission will probably not be constant enough for a reliable measurement b) when I’m routing the audio through the bluetooth headset, also the mic is routed. Since the mic and earphone of the headset can’t be moved independently, the current measurement method wouldn’t work.

  22. Sara Orsola Parolin says:

    Hello! I am a italian Physics teacher and I just posted an article on ‘the Physics Teacher’. In the classroom we used Acoustic Ruler Pro for an experiment. It Was fun. Title: Smartphone-aided measurements of the speed of sound in different gaseous mixtures

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