Air Pressure is the force exerted on you by the weight of tiny particles of air (air molecules). Although air molecules are invisible, they still have weight and take up space. Since there’s a lot of “empty” space between air molecules, air can be compressed to fit in a smaller volume. At sea level, the air pressure is about 14.7 pounds per square inch. Under a low pressure area, air is rising and as a result, the surface has less air molecules than before. Under a high pressure area, air is sinking towards the surface and piles up before spreading out.