Video tachometer 4+

Strobe light effect, RPM meter

Dmitriy Kharutskiy

    • 4.6 • 33 Ratings
    • Free
    • Offers In-App Purchases

iPhone Screenshots


When the frame rate of a video matches the speed of a particular part, the effect is the same as using a strobe light. In the video, that part freezes.

Since the frame rate of a video can be adjusted, this effect can be used to determine the rotational speed of a part.

The smartphone must support slow-motion video recording (filming at a high frame rate). This is the case for all smartphones starting with iPhone 5S. The range is as follows:

• 0.5—240 Hz (30—14400 RPM), for all phones from iPhone 6 onward
• 0.5—120 Hz (30—7200 RPM), for iPhone 5S


To get a clear image, good lighting is important. The clarity of the image is controlled by the exposure of the video (exposure time and light sensitivity (ISO)). If the exposure time is reduced, the image will increase in clarity, but brightness will lower. To increase the brightness, you need to raise the camera's light sensitivity (ISO), but then the amount of noise increases. You also need to manually adjust the focus of the camera.

Videos can be captured using the iOS "Screen Recording" function.

To take a photo with the result of the measurement written on it, press the "Pause" button and take a screenshot.

It is possible to choose a video format that has the best quality, but has a significantly lower maximum frame rate. The difference between the formats is clearly visible only when using the digital zoom. Also, when using a format with better quality, the Rolling Shutter effect is stronger. Therefore, the best quality format can be used at speeds less than about 1000 rpm.

You can turn on hints for easier observation of changes in rotation speed. Hints show how to change the frame rate (decrease or increase) depending on the direction of rotation of the mark. The hints are selected manually, but then you do not need to remember this information. The hints are relevant for frequencies close to the rotation frequency. If the direction of rotation of the impeller is known, hints can be selected in advance. The arrow showing the direction of rotation of the impeller must correspond to the "+" button.

The video tachometer measures the rotational speed in exactly the same way a stroboscopic tachometer would.

What’s New

Version 1.4

• Calculation of the rotation speed when the standard method has caused difficulties.
• Bug fixes.

Ratings and Reviews

4.6 out of 5
33 Ratings

33 Ratings

John_in_WI ,

Finally, one that works!

I’ve tried several apps that use the camera’s flashlight as the timing mechanism, which works fine if you’re in a darkroom and can be within 4” of your mark. Those apps have long since been deleted. Using the video frames per second is the way to go and now you can actually see your mark to know if you have your frequency set right. Thank you! Thank you! Thank you! This is the one you want.

Vincent7879 ,

Actually works!

I was about to go buy a tachometer when I remembered there were strobe light apps. This is stupid east to use and as long as you’re ok w/ 10 rpm increments you don’t need to pay anything.

I will say it’s a little hard to measure sub 200 RPM, although at that point you may be better off filming it in slow motion and counting the cycles

alwaysmprest ,

Doesn’t Use / Damage Flaslight

The explanation (by the developer) is pretty geeky, but the the idea is sound, and works!! (Note: the iPhone flashlight seems fairly durable, but one of the other actual strobes burned out a reviewer’s phone flashlight, which is the only camera flash!)
So: no use of flashlight except nice and steady light, as designed, to illuminate the rotating object.

App Privacy

The developer, Dmitriy Kharutskiy, indicated that the app’s privacy practices may include handling of data as described below. For more information, see the developer’s privacy policy.

Data Not Linked to You

The following data may be collected but it is not linked to your identity:

  • Diagnostics

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