Horizon Distance Calculator

Find how far the horizon is from your eye height. Includes the refraction-adjusted viewing distance and the maximum distance two objects of equal height can see each other.

Input

Enter your eye height (viewpoint elevation) to find the distance to the horizon.

Eye height preset

Pick a typical height or enter your own value.

Eye height (viewpoint elevation)

Height of your viewpoint above the reference surface.

Result

Distance to the horizon (with refraction)

4.722129km

The geometric distance without refraction is about 4.371842 km.

Geometric distance (no refraction)

4.371842 km

Mutual sight distance

9.444258 km

The mutual sight distance is the maximum distance at which two objects of the same height can see each other.

Using Earth mean radius 6371 km, the geometric distance is d = √(2Rh + h²). Refraction is included by scaling the effective radius by about 7/6.

How it works

Earth is treated as a sphere of mean radius R = 6371 km. From eye height h, the geometric distance to the horizon is d = √(2Rh + h²). When h is small compared with R, this is close to d ≒ √(2Rh).
Atmospheric refraction bends light, so the actual viewing distance is longer than the geometric distance. As a standard-atmosphere approximation, the effective Earth radius is taken as about 7/6 of the real radius. This refraction-adjusted value is the main result shown.
The mutual sight distance is the maximum distance at which two objects of the same height can see each other, equal to the sum of both horizon distances including refraction.
Eye height is the viewpoint elevation above the reference surface such as sea level. For views from a summit or tower, enter that elevation.
Terrain, obstacles, and weather-driven changes in refraction are not modeled. Values assume an ideal spherical surface and a standard atmosphere, so treat them as estimates.

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