Barometric pressure, also known as atmospheric pressure or air pressure, is the pressure exerted by the weight of the air molecules in the Earth's atmosphere at a given point

. It is the force per unit area that the air exerts on the surface below it. This pressure varies depending on altitude, weather, and temperature. At sea level, the average barometric pressure is about 14.7 pounds per square inch (PSI), or equivalently 1013.25 millibars (mb), 1013.25 hectopascals (hPa), or 29.92 inches of mercury (inHg)

. As elevation increases, the air becomes less dense and barometric pressure decreases because there is less air mass above the measurement point

. Barometric pressure changes with the weather and is used by meteorologists to predict short-term weather changes. For example, falling barometric pressure often indicates that rain or storms are likely, while rising pressure suggests clearer, sunnier weather

. Barometric pressure is measured using an instrument called a barometer, which traditionally uses a column of mercury to measure the pressure exerted by the atmosphere, though modern barometers often use electronic sensors

. In summary, barometric pressure is the measure of the weight of air above a specific location, influencing weather patterns and varying with altitude and atmospheric conditions