For a six-foot tall person, the horizon is a little more than 3 miles (5 km) away.
Geometry tells us that the distance of the horizon – i.e. the farthest point the eye can see before Earth curves out beneath our view – depends simply on the height of the observer. For example, if you stood atop Mount Everest (which is 29,029 feet, or 8,848 meters tall), the horizon would be about 230 miles (370 km) away.
So, in this picture, you are 3 miles away from the point in the curve that you can’t see the rest of the ocean past. And it is the same distance no matter what beach you are standing on, or what ocean you are looking at. I would know, I have travelled all over the world and looked at the horizon at the beach in every country I’ve gone too. It looks exactly the same everywhere. The curve is 3 miles away if your are six feet tall. The horizon is the fucking curve!!!