Flat vs. Round Earth Calculator

Your details

Choose which observable phenomenon to model. Each uses a different set of inputs.
Height of your eyes above the water or ground surface.
m
Horizontal distance from you to the object (ship, tower, lighthouse).
km
Total height of the object (ship mast, lighthouse, tower).
m
Curvature drop (round Earth)Partially hidden by curvature
31.39

How far the surface curves below a straight line at the target distance

Horizon distance5.05
Hidden height (round Earth)17.54
Hidden height (flat Earth)0
Round Earth prediction48.94
Flat Earth prediction0

Difference: 48.94 (Round Earth prediction higher)

  • Curvature drop
  • Object hidden
  • Circumference
  • Extra sunset (s)
  • Second sunset visible

Curvature drop over this distance: 31.39 m

  • Your horizon is 5.05 km away from your 2.0 m vantage point.
  • The Earth's surface curves 31.39 m below a straight horizontal line at that distance.
  • On a flat Earth, none of the object would be hidden by curvature, no matter how far away it is.

Next stepThe bottom 17.54 m of the object is hidden behind the horizon. A flat Earth cannot explain this disappearance.

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