Calculate distance to the horizon and how much of a distant object is hidden by Earth's curve.
Observer & Target
Curvature Results
Enter height and distance
About this calculator
Quick Reference
R6,371 km (Earth Radius)
h1Observer eye level
dGeometric horizon distance
h2Hidden height of target
Overview
This calculator estimates how much of a distant object is hidden by the Earth's curvature, assuming a spherical Earth with a radius of approximately 6,371 km.
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Pro Tips
Standard atmospheric refraction can make objects appear higher than they are, allowing you to see roughly 7% further than the geometric horizon.
The geometric horizon distance is d = sqrt(2 * R * h + h²).
If the target is beyond the horizon, the hidden part is approximately (Distance - Horizon)² / (2 * R).
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Fun Facts
"The '8 inches per mile squared' rule is a popular approximation for the hidden height for short distances."
"Light refraction in the atmosphere often allows us to see 'around' the curve slightly."
"The ancient Greeks, like Eratosthenes, proved the Earth was a sphere and even calculated its circumference over 2,000 years ago."
