At sea level, the approximate value of atmospheric pressure in those units of measure is as follows:
- 101.3 kPa which is how it is usually expressed. In pascals, it is 101325 pascals. The first of these units (kilopascals) is usually used because pascals are such a small unit that it is much less cumbersome to express the measurement in kilopascals.
- In mmHg (milimeters of mercury), the measure is 760
- In atm (atmospheres) it is 1 atm.
These are a standard set of measures. The actual measurement will, of course, vary with weather conditions, which is why barometers work.
Although 1013.25 mb (760 mm Hg) is considered to be the standard atmospheric pressure at sea level, it does not mean that the pressure at this level has this value, actually this being 1011 mb.
Since much of the Earth's surface is above sea level, annual average atmospheric pressure at the surface was estimated to be 984.43 mb.
Atmospheric pressure measurement is made by direct reading on barometer with mercury or metal barometer. The registration of atmospheric pressure is made with Barograph, daily or weekly.In situations where the weather is the distribution of atmospheric pressure at sea level, to the values determined instrumental will suffer correction of level (height=0m and t=150C), temperature correction(reducing to 0C) and correction of latitude(reducing to the average latitude).
Atmospheric pressure is encoded being reduced at sea level, in mb, symbol PPPP (± 0.1 mb).
The atmospheric pressure at the sea level is equal to 760 mm of height of the column of mercury. With this height of 760 mm of mecury, the atmospheric pressure is equal to the weight force of the 760 mm of mercury. So, the pressure P = weight of mecury of occupying a cuboid of 1 sq meter base and height of 0.76 meter = 0.76 cubic meter* density of mecury*10N/Kg
=(0.76cubic meter.)(13534 Kg/cb met)(10N/kg) / sq meter.
=116690.4 N/sq meter.
=116690.4 pascals, is the atmospheric pressure at the sea level, where the acceleration due to gravity is 10N/kg.This is slightly more, as we are to work for the pressure at the location of the sea level where g = 10N/kg,