Earth Curvature Calculator

This tool applies the geometry of a sphere the size of the earth to three questions: how far the surface falls away from a level line, how far off the horizon is for a given eye height, and how much of a distant object is cut off by the curve. Enter a distance, or an eye height, or both together with the height of the thing you are looking at. Answers come back in feet and metres, with the radius used and the formula printed alongside. Standard atmospheric refraction can be switched on, which repeats the same geometry on a sphere 7/6 as large. It assumes a smooth sphere at sea level, so terrain, waves and unusual air will move the real answer.