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The average pressure at mean sea level in the International Standard Atmosphere is 1,013.25 hPa, or 1 atmosphere (atm), or 29.92 inches of mercury. Pressure (P), mass (m), and acceleration due to gravity (g) are related by P = F/A = (m*g)/A, where A is the surface area.
Barometric pressure is measured either in millibars (mb) or inches of mercury (Hg). Readings below 29.80 Hg are often considered as low barometric pressure, whiles readings above 30.20 Hg are considered high; readings within the range of 29.9 Hg to 30.2 Hg are considered normal.
The most basic change in pressure is the twice daily rise and fall due to the heat from the sun. Each day, the pressure is at its lowest around 4 a.m./p.m., and at its highest around 10 a.m./p.m. The magnitude of the daily cycle is greatest near the equator, decreasing toward the poles.
The standard barometric pressure at sea level is 29.92 inches (1,013 millibars) of mercury (also measured as 1 atmosphere). In general, a normal range for barometric pressure is between 28.5 (965 millibars) and 30.7 inches (1,040 millibars) of mercury.
Atmospheric pressure is the force per unit area exerted by a body of air above a specified area (called an atmospheric column). It is expressed in several different systems of units, including millimeters (or inches) of mercury, pounds per square inch (psi), millibars (mb), or standard atmospheres.
The definition of STP - Standard Temperature and Pressure and NTP - Normal Temperature and Pressure. U.S. Standard Atmosphere vs. Altitude Properties of the US standard atmosphere ranging -5000 to 250000 ft altitude. Vacuum Vacuum is defined as air pressure below atmospheric pressure.
An atmosphere (atm) is a unit of measurement equal to the average air pressure at sea level at a temperature of 15 degrees Celsius (59 degrees Fahrenheit). One atmosphere is 1,013 millibars , or 760 millimeters (29.92 inches) of mercury.