A recently developed iPhone app called My Jump ($5.99), measures vertical jump height (VJ) and has been tested by researchers showing strong test validity and reliability, compared to a force platform, on college students. The research study was published in the Journal of Sports Sciences and the lead investigator, Carlos Balsalobre-Fernandez is actually one of the co-developers of the app. There are various ways to measure VJ but using a force platform is considered the gold standard by many strength and conditioning coaches.
The app works by taking a picture of the person or athlete while doing a counter movement jump. One of the new update features in the iPhone (starting back with the iPhone 5s) is a high-speed camera that is capable of recording 120 Hz. By using the camera and My Jump app, the phone now has the ability to capture high-speed videos and subsequently calculate VJ.
Here is a diagram from a recent Twitter post on @myjumpapp from Carlos Balsalobre demonstrating the strong correlation with the My Jump app compared to a force platform.
In terms of possible applications, this could be a new in the tool box for strength and conditioning coaches, personal trainers, students and the average workout enthusiast, to help measure and monitor lower body power output.
Here is a website that shows how to do more of a traditional VJ test but you can use the site and the normative data to look at how your own VJ rates (in inches and cm).
Carolos Balsalobre-Fernandez et. al., The validity and reliability of an iPhone app for measuring vertical jump performance. Journal of Sports Sciences, 2014
Is the Vertical Jump the Best Measure of Power? by Bryan Mann, PhD, Assistant Director, Strength and Conditioning, University of Missouri.