Thunder Distance is a very useful app for calculating the distance between your current location and the thunder.
You can view and share the three most recent results.
When you see a lightning flash outside, tap on the Light/Flash button in the app. When you hear the thunder, tap on the Sound/Thunder button. The app will give you a distance in Meters, Kilometers, Miles and Yards.
There are 12 different backgrounds available to choose from. There is also a Help page with a small explanation of the basic controls in the app.