At sea level, what is the approximate value of atmospheric pressure in Pa, in mmHg and in atm? (where g = 10 N/kg)

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).