Air - Altitude, Density and Specific Volume The density and the specific volume of air varies with the elevation above sea level Sponsored Links
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 (m)
Barometer (mmHg)
0
760
75
753
150
746
250
739
300
733
450
719
600
706
750
693
900
681
1,000
668
1,200
656
Altitude (m)
Barometer (mmHg)
1,350
644
1,500
632
1,800
609
2,100
586
2,400
564
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 0oC 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 20oC and 101.6 kN/m2 (68oF, 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 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
Altitude and Air Pressure Altitude
Pressure
Feet
Meter
inHg
torr
psia
kPa
0
0
29.92
759.97
14.7
101.3
500
152
29.39
746.51
14.43
99.4
1000
305
28.86
733.04
14.17
97.6
1500
457
28.34
719.84
13.91
95.8
2000
610
27.82
706.63
13.66
94.1
2500
762
27.32
693.93
13.41
92.4
Altitude
Pressure
Feet
Meter
inHg
torr
psia
kPa
3000
914
26.82
681.23
13.17
90.7
3500
1067
26.33
668.78
12.93
89.1
4000
1219
25.84
656.34
12.69
87.4
4500
1372
25.37
644.4
12.46
85.8
5000
1524
24.9
632.46
12.23
84.3
5500
1676
24.44
620.78
12
82.7
6000
1829
23.98
609.09
11.77
81.1
6500
1981
23.53
597.66
11.55
79.6
7000
2134
23.09
586.49
11.34
78.1
7500
2286
22.66
575.56
11.13
76.7
8000
2438
22.23
564.64
10.91
75.2
8500
2591
21.81
553.97
10.71
73.8
9000
2743
21.39
543.31
10.5
72.3
9500
2896
20.98
532.89
10.3
71.0
10000
3048
20.58
522.73
10.1
69.6
10500
3200
20.19
512.83
9.91
68.3
Altitude
Pressure
Feet
Meter
inHg
torr
psia
kPa
11000
3353
19.8
502.92
9.72
67.0
11500
3505
19.41
493.01
9.53
65.7
12000
3658
19.03
483.36
9.34
64.4
12500
3810
18.66
473.96
9.16
63.1
13000
3962
18.3
464.82
8.99
61.9
13500
4115
17.94
455.68
8.81
60.7
14000
4267
17.58
446.53
8.63
59.5
14500
4420
17.24
437.9
8.46
58.3
15000
4572
16.89
429.01
8.29
57.1
15500
4724
16.56
420.62
8.13
56.0
16000
4877
16.22
411.99
7.96
54.8
16500
5029
15.9
403.86
7.81
53.8
17000
5182
15.58
395.73
7.65
52.7
17500
5334
15.26
387.6
7.47
51.5
18000
5486
14.95
379.73
7.34
50.6
18500
5639
14.65
372.11
7.19
49.5
Altitude
Pressure
Feet
Meter
inHg
torr
psia
kPa
19000
5791
14.35
364.49
7.05
48.6
19500
5944
14.05
356.87
6.9
47.5
20000
6096
13.76
349.5
6.76
46.6
20500
6248
13.48
342.39
6.62
45.6
21000
6401
13.2
335.28
6.48
44.6
21500
6553
12.92
328.17
6.34
43.7
22000
6706
12.65
321.31
6.21
42.8
22500
6858
12.38
314.45
6.08
41.9
23000
7010
12.12
307.85
5.95
41.0
23500
7163
11.86
301.24
5.82
40.1
24000
7315
11.61
294.89
5.7
39.3
24500
7468
11.36
288.54
5.58
38.4
25000
7620
11.12
282.45
5.46
37.6
25500
7772
10.88
276.35
5.34
36.8
26000
7925
10.64
270.26
5.22
36.0
26500
8077
10.41
264.41
5.11
35.2
Altitude
Pressure
Feet
Meter
inHg
torr
psia
kPa
27000
8230
10.18
258.57
5
34.5
27500
8382
9.96
252.98
4.89
33.7
28000
8534
9.74
247.4
4.78
32.9
28500
8687
9.53
242.06
4.68
32.2
29000
8839
9.31
236.47
4.57
31.5
29500
8992
9.11
231.39
4.47
30.8
30000
9144
8.9
226.06
4.37
30.1