Density Altitude Calculator
- using selectable units and relative humidity -
Example 1: at 5050 feet elevation, 95 deg F, 29.45 inches-Hg barometric pressure and 40% relative humidity, the Density Altitude is calculated as 9251 feet.
Example 2: at 1540 meters elevation, 35 deg C air temp, 997 hPa barometric pressure and 40% relative humidity, the Density Altitude is calculated as 2824 meters.
Air density is affected by the air pressure, temperature and humidity. The density of the air is reduced by decreased air pressure, increased temperatures and increased moisture. A reduction in air density reduces engine horsepower, reduces aerodynamic lift and reduces drag.
The National Weather Service (NWS) has on-line relative humidity and altimeter setting for a variety of US locations, in both English and Metric units. Also, the Federal Aviation Administration (FAA) offers local phone numbers for AWOS data at many US airports.
The metric unit hPa (hectoPascal) is identical to the pressure unit called mb (milliBar).
Drag racers and engine tuners... take a look at the features in the Engine Tuner's Calculator. The engine tuner's calculator includes relative horsepower, air density, density altitude, virtual temperature, absolute pressure, vapor pressure, relative humidity and dyno correction factor.
Elevation (also called Altitude) is the geometric elevation above mean sea level.
Air Temperature is the measured air temperature.
Altimeter Setting is the value in the altimeter's Kollsman window when the altimeter is set to correctly read a known elevation.
Relative Humidity is the ratio of the partial pressure of water vapor to the saturated vapor pressure at a given temperature.
Note: The calculator which uses Dew Point is often more accurate because the dew point is fairly constant for a given air mass and changes very little until another air mass arrives, while the relative humidity varies greatly as the ambient temperature changes.
Density Altitude is the altitude in the International Standard Atmosphere which has the same density as the air being evaluated.
Note: The ICAO International Standard Atmosphere standard conditions for zero density altitude are 0 meters (0 feet) altitude, 15 deg C (59 deg F) air temp, 1013.25 mb (29.921 in Hg) pressure and 0 % relative humidity (no water vapor in the air).
Note: If the calculated air density is less than the standard sea level air density, the calculator will show a negative altitude, that is, an altitude below sea level, which is merely the result of a mathematical extrapolation of the standard atmosphere, even though such an altitude may not exist in free-air.
Absolute Pressure is the actual air pressure, not corrected for altitude, and is also called the station pressure.
Air Density is the mass per unit volume of the air. For example, the standard air density at sea level is 1.225 kg/m3 (0.076474 pounds/ft3).
Relative Density is the ratio of the actual air density to the standard sea level density, expressed as a percentage.
Estimated AWOS uses equations from the US National Weather Service to calculate approximately the same density altitude as reported by the current ASOS and AWOS-3 automated weather observation stations which are in widespread use around the US, most commonly located at (or near) airports.
Note: Due to rounding of decimal values, the AWOS estimate on this page may occasionally differ from the ASOS/AWOS-3 reported density altitude, but is generally within ± 100 feet. The current ASOS/AWOS-3 reports apparently do not account for the moisture content of the air, and are therefore somewhat lower than the actual Density Altitude (as shown by this calculator) when the relative humidity is high. Also, note that ASOS/AWOS-3 stations only report density altitude when it is more than 1000 feet greater than the station elevation, and the reported value is rounded to the nearest 100 feet.
For more technical details about the calculations that determine density and density altitude, take a look at my Density Altitude page.
Copyright 1998-2012, All Rights Reserved, Richard Shelquist, Shelquist Engineering.
Last Updated: 3-Apr-2012