Air - Density and Specific Volume vs. Altitude
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:
| 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:
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
| 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 | metre | 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 |
| 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
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
Related Topics
• Air Psychrometrics
Moist and humid air - psychrometric charts, Mollier diagrams, air-condition temperatures and absolute and relative humidity and moisture content.
• Densities
Densities of solids, liquids and gases. Definitions and convertion calculators.
• Fluid Mechanics
The study of fluids - liquids and gases. Involving velocity, pressure, density and temperature as functions of space and time.
• Gases and Compressed Air
Air, LNG, LPG and other common gas properties, pipeline capacities, sizing of relief valves.
• Material Properties
Material properties of gases, fluids and solids - densities, specific heats, viscosities and more.
• Ventilation
Systems for ventilation and air handling - air change rates, ducts and pressure drops, charts and diagrams and more.
Related Documents
Air - Density vs. Pressure and Temperatures
Air density at pressure ranging 1 to 10 000 bara (14.5 - 145000 psi) and constant selected temperatures.
Air - Density, Specific Weight and Thermal Expansion Coefficient vs. Temperature and Pressure
Online calculator, figures and tables showing density, specific weight and thermal expansion coefficients of air at temperatures ranging -100 to 1600 °C (-140 to 2900 °F) at atmospheric and higher pressure - Imperial and SI Units.
Air - Thermophysical Properties
Thermal properties of air at different temperatures - density, viscosity, critical temperature and pressure, triple point, enthalpi and entropi, thermal conductivity and diffusivity and more.
Air - Volume vs. Temperature
Air volume vs. temperature correction factor compared to Normal Air Conditions.
Air Temperature, Pressure and Density vs. Altitude
Elevation above sea level and air temperature, pressure and density.
Atmospheric Pressure vs. Elevation above Sea Level
Elevation above sea level - in feet and meter - with barometric and atmospheric pressure - inches mercury, psia, kg/cm2 and kPa.
Barometer - Altitude Compensation
Elevation compensating manometer.
Dry Air - Thermodynamic and Physical Properties
Thermodynamic properties of dry air - specific heat, ratio of specific heats, dynamic viscosity, thermal conductivity, Prandtl number, density and kinematic viscosity at temperatures ranging 175 - 1900 K.
Dry Air and Water Vapor - Density and Specific Volume vs. Temperature - Imperial Units
Density and specific volume of dry air and water vapor at temperatures ranging 225 to 900 degF (107 to 482 degC).
STP - Standard Temperature and Pressure and NTP - Normal Temperature and Pressure
The definition of STP - Standard Temperature and Pressure and NTP - Normal Temperature and Pressure.
U.S. Standard Atmosphere vs. Altitude
Properties of the US standard atmosphere ranging -5000 to 250000 ft altitude.
Wind Power
Power generation from wind.