how far away is the horizon

The distance to the horizon depends primarily on the height of the observer above the Earth's surface. For an average person standing at sea level with eyes about 1.5 to 1.75 meters above the ground, the horizon is roughly 3 miles (about 5 kilometers) away. This is based on the geometry of a sphere and can be estimated using the formula d=2Rhd=\sqrt{2Rh}d=2Rh​, where RRR is the Earth's radius (about 6,371 km) and hhh is the observer's height above the surface. If the observer's height increases, such as standing on a tall building, mountain, or even flying in an airplane, the horizon distance increases accordingly—for example, from the top of a 100-meter tower, the horizon can be about 36 kilometers (22 miles) away. In summary, the horizon distance varies with height but is about 3 miles or 5 kilometers for a person standing at ground level by the sea.