Inches of mercury (inHg) is a unit of pressure commonly used in meteorology and aviation. It measures how high a column of mercury can be pushed up by atmospheric pressure. One inch of mercury is equivalent to the pressure exerted by a one-inch column of mercury at standard gravity. This measurement is often used in barometers, which are instruments that measure atmospheric pressure. The standard atmospheric pressure at sea level is about 29.92 inches of mercury. Changes in inHg readings can indicate weather changes, such as approaching storms or fair weather conditions.