What is Earth's surface (sea level)? Its pressure is 14.7 psi. That is what is the number of ft.

Answer 1

14.7 psi is the air pressure at the earth's surface. That is the pressure exerted by a 1-sq-in column of air reaching up to space.

The earth's atmosphere is about 300 miles thick. That air presses down everywhere with a weight of 14.7 pounds on every square inch of the surface.