Air - Altitude, Density and Specific Volume

The density and the specific volume of air varies with the elevation above sea level

The density of air will vary with the 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 (m)	Barometer (mmHg)
0	749
75	743
150	735
250	726
300	723
450	709
600	695
750	681
900	668
1,000	658
1,200	643
1,350	632
1,500	620
1,800	598
2,100	577
2,400	555

Altitude and Air Density

Air density and specific volume as functions of altitude above sea level are indicated 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 (60^oF , 30 in Hg)

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		Volume Correction Factor
(m)	(ft)
0	0	1.00
480	1600	1.05
990	3300	1.11
1500	5000	1.17
1980	6600	1.24
2460	8200	1.31
2970	9900	1.39

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