Flat vs. Round Earth Calculator
Compute expected curvature drop and horizon distance for a spherical Earth model.
How to Use This Calculator
Enter distance
Provide the line-of-sight or surface distance between observer and target in kilometers.
Set Earth radius and observer height
Use R = 6371 km by default. Add your eye height to estimate geometric horizon.
Compare outcomes
If the target is below the curvature drop and beyond horizon, it won’t be visible without refraction.
Formula
\u0394h \u2248 d^2/(2R), d_h \u2248 \u221a(2Rh + h^2)
Where: \u0394h is curvature drop (m), d is distance (m), R is Earth radius (m), d_h is horizon distance (m), h is observer height (m).
These are standard geometric approximations valid for d \u226a R.
About Flat vs. Round Earth Calculator
This tool shows measurable geometric consequences of a spherical Earth: curvature drop over distance and the distance to the horizon from a given eye height.
Common Applications
- Photography over water and distant skyline visibility.
- Line-of-sight checks for towers and observation points.
- Educational demonstrations on Earth geometry.
Frequently Asked Questions
Does refraction affect visibility?
Yes. Atmospheric refraction can bend light downward, extending visibility slightly beyond the geometric horizon.
Is the drop formula exact?
It’s a small-distance approximation. For very long distances, use exact spherical geometry.
Do elevation changes matter?
Yes. Terrain and object height relative to sea level affect actual line-of-sight.