Earth’s atmosphere extends approximately 100 kilometers (328,000 feet) above the ground, but it gets less and less dense as the altitude increases. If the density were constant, then the atmosphere would be about 8-kilometers high (26,246 feet; close to the height of Mt. Everest). Some 63% of the atmosphere is below that height. The amount of force on an area of one square meter is about 101,300 newtons. That is, the pressure is 101.3 kPa. Atmospheric pressure varies with temperature and other conditions. Our weather is mostly influenced by high and low pressure regions, which can deviate by about 5% from normal.

The pressure decreases as your altitude increases because the amount of air above you creating the pressure is smaller. At an altitude of 3 kilometers (10,000 feet) above sea level the atmospheric pressure is about 70% of what it is at sea level. At 100 kilometers it is 3 millionths of the sea level pressure!