Q:  What is the average air pressure at the surface of the Earth?

A:  The standard, or near-average, atmospheric pressure at sea level on the Earth is 1013.25 millibars, or about 14.7 pounds per square inch. The gauge pressure in my automobile tires is a little more than twice that value. If you live at a higher altitude, the pressure will be lower since there is less air above weighing down upon you. The pressure also varies by relatively small amounts as high and low pressure systems move past.

--Michael Bell