Normal temperature is 25 degrees, a standard atmospheric pressure is 101kPa (760mm Hg), room temperature 25-27 degrees Celsius, normal temperature and normal pressure is the set of normal temperature and a standard atmospheric pressure . (Two conditions)

Standard temperature and pressure (STP) was once defined in chemistry as 0°C (273.15K) and 101.325kPa (1atm), but since 1982 IUPAC has redefined "standard pressure" as 100 kPa.

1 Standard atmospheric pressure = 760mm Hg = 76cm Hg = 1.01325×10^5Pa = 10.339m water column. 1 standard atmospheric pressure = 101325 N/m2. (In calculations it is usually 1 standard atmospheric pressure = 1.01×10^5 N/m2). 100kPa = 0.1MPa

Expanded:

Changes in atmospheric pressure are related to altitude. Atmospheric pressure is created by the atmosphere being subjected to gravity, and the higher you are from the ground, the thinner the atmosphere is, and the less atmospheric pressure there should be. However, since the density of the air, which is related to the gravitational force on the atmosphere, varies unevenly with height, the decrease in atmospheric pressure with height is also uneven. Variation with height: Atmospheric pressure decreases with height.

Changes in atmospheric pressure are also related to weather. Atmospheric pressure is not exactly the same in the same place at different times. We know that the density of water vapor is smaller than the density of air, when the air contains more water vapor, the density of air to become smaller, the atmospheric pressure is also reduced.

When the air is cooled, the air shrinks, the density increases, the weight of the air column borne on the unit area increases, and the air pressure rises. Therefore, the arrival of cold air is always accompanied by an increase in air pressure, while the arrival of warm air, the air pressure will decrease again. Winter is the world of cold air, summer is the world of warm air, air pressure winter high summer low reason is also clear.

Baidu Encyclopedia - Standard Atmospheric Pressure