Assuming everything is flat (or more precisely visible) around, how far is the horizon from where I stand? Approximately?

I know, it can be mathematically calculated, but I’m just lazy now.

And, how much area would that be that I can see all around me 360 degrees? What is the shape of the area called? I imagine the shape like cornea of the human eye or a contact lens.

Topics: astronomy, mathematics, distance, trigonometry, area, horizon