You can not calculate for the curvature as there is no curvature. There is not a single proof of curvature existing. As I said before look on youtube, amateur weather balloons are sent 120,000 feet up and they show a perfectly flat horizon rising to eye level of the camera, proving for a FACT that either earth is flat and endless plane or earth as a planet is atleast 100 or 1000 times larger than it is claimed to be.