This height calculator is a totally free application, no in-app purchase is required and has a large number of applications.
Also keep in mind the mass of the object. Measurements can vary depending on how heavy is the object. Therefore it is recommended to use a small stone, coins, or a golf ball.
I wanted to share the app but didn't have a button to share, so, do it from Play store only. I tested the app from a 40 feet height, dropped a rock and was very accurate. I measured a 3 ft drop too and got me a very close number. For an app that doesn't take in consideration a lot of things is really accurate. MUST BE SOMETHING SOLID ONLY!