Calculate the Distance to the Horizon

Calculator for the distance to the horizon at clean air and with nothing standing in the way. View height is the height of the eyes above ground. When the eye height is at 1.70 m and the viewer stands on a 20 m high tower, the view height a = 21.70 m. When a high object, e.g. a mountain or a ship, protrudes behind the horizon, then b is its height above ground and c is the distance to this object.

Formulas:

c = f * ( √a + √b )
The unit of f is 1000 * √m

f = √2R
R is the mean Earth radius in 1000 km, 6.371.
With atmospheric refraction, as R is taken the mean apparent Earth radius of 7.68.

You can convert length units here.

View height a:		m
Object height b:		m
Distance c:		km