🌅 Curvature of the Earth Line-of-Sight Calculator
Enter observer height (and optionally a target’s height) to calculate how far you can see before the Earth’s curvature blocks the view, including a standard refraction correction.
Why the Earth’s curvature limits visibility
Because the Earth is curved, an observer’s view is eventually blocked by the horizon. The higher up you are, the farther you can see before the surface curves away.
The formula
Distance to the horizon from a height h is d = √(2Rh), where R is Earth’s radius (6,371 km). This calculator applies a standard atmospheric refraction correction by using an effective Earth radius of 7/6 times the true radius, since light bends slightly downward through the atmosphere, letting you see a bit farther than pure geometry alone would suggest. If you enter a target height too (like a distant tower or ship’s mast), the calculator adds both horizon distances together for total line-of-sight range.
The refraction correction is a standard approximation that assumes typical atmospheric conditions; unusual temperature layering (like a temperature inversion) can extend or reduce real visibility further. This calculator is for general reference and educational purposes.