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Air - Density and Specific Volume vs. Altitude

Density and specific volume of air varies with elevation above sea level.

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 barometer pressure varies with altitude as shown in the table below:

Air - Pressure vs. Altitude
Altitude
(m)
Pressure
(mmHg)(kPa)
0 760 101.3
75 753 100.4
150 746 99.5
250 739 98.5
300 733 97.7
450 719 95.9
600 706 94.1
750 693 92.4
900 681 90.8
1000 668 89.1
1200 656 87.5
1350 644 85.9
1500 632 84.3
1800 609 81.2
2100 586 78.1
2400 564 75.2

Altitude and Air Density

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

Air - altitude, density and specific volume

air altitude feet density and specific volume diagram

 

STP - Standard Temperature and Pressure

  • STP - Standard Temperature and Pressure is 273.15 K (0 °C, 32 °F) and absolute pressure exactly 105 Pa (100 kPa, 1 bar) - according IUPAC - International Union of Pure and Applied Chemistry - since 1982 

NTP - Normal Temperature and Pressure

  • NTP - Normal Temperature and Pressure (commonly used for testing and documentation of fan capacities) is  293.15 K (20 °C, 68 °F) and absolute pressure 1 atm (101.325 Pa, 14.696 psi) according NIST - National Institiute of Standards and Technology 

Note! - other definitions of STP and NTP are widely 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

Air - Volume Correction vs. Altitude
AltitudeVolume
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

Air - Pressure vs. Altitude
AltitudePressure
feetmetreinHgtorrpsiakPa
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
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
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
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
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

Temperature vs. Elevation Density Correction

Air density - elevation density versus temperature correction factor

The chart above can be used to estimate "temperature vs. elevation density correction factor". The density at a given temperature and elevation can then be calculated as

ρ = ρref / f                               (1)

where

ρ = density at the given temperature and elevation (lbm/ft3)

ρref = density reference at elevation 0 ft and temperature 70 oF  - (0.075 lbm/ft3)

f = correction factor from the chart above

Example - Density at Elevation 4000 ft and Temperature 300 oF

From the chart above - at elevation 4000 ft and temperature 300 oF the correction factor is approximate 1.7. The density can be calculated as

ρ = (0.075 lbm/ft3) / 1.7

   = 0.043 lbm/ft3  

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