How far from the shore can you see until the horizon?

According to Maryln Van DeSavant I seem to recall she said 7 miles. From basic geometry, you get that the distance to the horizon is D=sqrt(2Rh) where D = distance to horizon R = radius of earth h = height of observer, which would be the height of your eyes. R and h have to be in consistent units, of course. In feet the radius of the earth is about 4000 mi * 5000 ft/mi or 20 million feet. Standing on the shore, your eyes are maybe 5 feet above the surface, so D=sqrt(2*20e6*5)= 14000 feet, or a little under three miles. There are some other effects that make that number a little different. Refraction bends your line of sight, so you can see a little bit farther. If you're looking at an object on the water, like a ship, you also get the distance on the other side of the horizion that corresponds to the height of the target. ==How to calculate the distance yourself== To get an "approximate" distance to the oceanic horizon from a particular observation point, take the square root of the height of the observation point, add 22.5%, and that will give you the distance in statute miles. For example, if your eyes were 6 feet off the ground, and you stood atop a 50' tower, your observation point would be 56'. The square root of 56' is 7.48. Add 22.5% of 7.48 (1.68) to 7.48 and you have 9.16 statute miles from your eyes to the horizon.