At above sea level what is the approximate value of atmospheric pressure?

Pressure is defined as force acting on an area, or force per unit area. What we call atmospheric pressure is caused by the weight of the atmosphere. Several different units are used for pressure, including millimeters of mercury (mmHg), torr, which is numerically equal to mmHg, atmospheres (atm), pascals (Pa) and kilopascals (kPa), and pounds per square inch. Pounds per square inch is least commonly used in science, but is helpful in that it conveys the idea of the weight of the atmosphere (a force) pressing on a specific area.
Atmospheric pressure varies with the weather, but an average can be found. The average atmospheric pressure at sea level is 14.7 pounds per square inch, or 760 mmHg = 760 torr, or 101,325 Pa, or 1.00 atm.
Above sea level, one is no longer at the bottom of the whole column of air. Some of the air is lower. Pressure is caused by the weight of the air above. The greater the altitude above sea level, the less air is above. Thus less weight is pushing down, and the observed pressure is less. The Engineering Toolbox (link included) gives a function for the pressure at any altitude (in Pa)
p = 101325 (1 - 2.25577*10^(-5)h)^(5.25588)
where h is the altitude in meters.
In science, "weight" specifically means the force due to gravity acting on a mass. The force of gravity is constant, and the mass of air above decreases as one goes up from sea level (and is therefore above some of the air). Thus we can say that the weight, or force, decreases with increasing altitude.
https://www.engineeringtoolbox.com/air-altitude-pressure-d_462.html