Density Altitude Calculator - selectable units

Density altitude is defined as the altitude in the International Standard Atmosphere that has the same air density as the air being evaluated.

To use the calculator, just click the type of units that you will be entering, then enter the altitude, temperature, altimeter setting and dew point... then click the calculate button.
 

Additional Information:

Click here for National Weather Service (NWS) information, including listing of hourly dew point and altimeter setting for US locations, in both English and Metric units.

Example 1:  at 5050 feet elevation, 95 deg F air temp,  29.45 inches-Hg barometric pressure and a dew point of 67 deg F, the Density Altitude is calculated as 9252 feet.

Example 2:  at 1540 meters elevation, 35 deg C air temp,  997 hPa barometric pressure and a dew point of 19 deg C, the Density Altitude is calculated as 2821 meters.

The metric unit hPa (hectoPascal) is identical to the pressure unit called mb (milliBar).

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 the engine horsepower, reduces aerodynamic lift and reduces drag.

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.

Input Values:

The elevation (or altitude) is the geometric elevation above mean sea level, and is the elevation at which the altimeter setting, temperature and dew point have been measured.

The altimeter setting is the value in the altimeter's Kollsman window when the altimeter is set to correctly read a known elevation. The altimeter setting is generally included in NOAA weather data reports. (For more information about ambient air pressure measurements see the pressure measurement page.)

This calculator uses dew-point rather than relative humidity because the dew point is fairly constant for a given air mass, while the relative humidity varies greatly as the temperature changes.

Output Values:

Density Altitude is the altitude in the International Standard Atmosphere that has the same density as the air being evaluated.

Absolute Pressure is the actual air pressure, not corrected for altitude, and is also called the station pressure.

Relative Density is the ratio of the actual air density to the standard sea level density, expressed as a percentage. The standard sea level air density is 1.225 kg/m³ (0.002378 slugs/ft³), and 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 (absolute zero dew point).

Estimated AWOS uses equations from the US National Weather Service which give approximately the same density altitude as reported by the current ASOS and AWOS-3 automated weather observation stations which are in common use around the US. Due to rounding of decimal values, the AWOS estimates on this page may occasionally differ from the ASOS/AWOS-3 reported density altitude, but are generally within ± 100 feet. Please note that 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. When the humidity is high, the ASOS/AWOS-3 reported density altitude may be 20 to 30% less than the actual Density Altitude (as shown by this calculator). (Note that ASOS/AWOS-3 stations report density altitude only when it is more than 1000 feet greater than the station elevation, and the reported value is rounded to the nearest 100 feet.)

Resources:

For more technical details about the calculations that determine density and density altitude, take a look at my Density Altitude page. 

A useful source for simple atmospheric theory, explanations and calculations is the USA Today Weather web site. Also, there are several conversion calculators available from El Paso NWS.

Disclaimer:  This calculator is for educational purposes only and should not be relied upon for flight planning.

Copyright 1998-2010,  All Rights Reserved, Richard Shelquist, Shelquist Engineering.

Last Updated: 3-Jul-2010