Air - Altitude, Density and Specific Volume

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The density of air varies with pressure (the Ideal Gas Law) and the altitude above sea level. Mean absolute pressure at sea level is approximately 760 mmHg (101.325 kPa, kN/m²) with a variation is about +/- 5%.

Altitude and Air Pressure

The air pressure varies with altitude as shown in the table below:

Altitude and Air Density

Air density and specific volume as functions of altitude above sea level can be indicated as in the diagrams below:

STP - Standard Temperature and Pressure

• STP - Standard Temperature and Pressure is 0^oC and 101.325 kN/m².

NTP - Normal Temperature and Pressure

• NTP - Normal Temperature and Pressure, commonly used for testing and documentation of fan capacities, is 20^oC and 101.6 kN/m² (68^oF, 30 in Hg)

Note! - other definitions of STP and NTP are commonly used.

Altitude and Specific Volume Correction

The specific volume of standard air at a certain altitude can be calculated by multiplying with the volume correction factor below

Altitude and Air Pressure

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