Earth Curvature Calculator

Your details

Horizontal distance from the observer to the target along the surface.
km
Height of the observer's eyes above mean sea level (or above the surface if standing on flat ground).
m
Height of the target object (e.g. a building, cliff, or ship mast). Used to compute required observer height.
m
Atmospheric refraction bends light slightly downward, making the effective Earth radius larger and extending visibility. k = 0.13 is the accepted average for standard atmosphere.
Curvature dropNoticeable curvature
6.828

Vertical distance the surface falls away below a straight line over the given distance.

Drop unitm
Hidden height1.71
Hidden height unitm
Horizon distance4.99
Horizon distance unitkm
Required observer height0
Required observer height unitcm
Effective Earth radius7,322,989
Drop6.828
Hidden height1.71

Curvature drop over 10 km: 6.828 m

  • Over 10 km, Earth's surface curves away by 6.828 m.
  • A target at that distance has its bottom 1.71 m hidden below the horizon when viewed from your eye height.
  • Your horizon is approximately 4.99 km away at the given eye height.
  • Atmospheric refraction is included, which bends light slightly and extends visibility beyond the geometric horizon.

Next stepFor surveying or photography, use the "required observer height" output to plan how high you need to be to see your target over the curvature.

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