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