Density Altitude Calculator - with Relative Humidity

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 this calculator,  just enter the altitude, temperature, altimeter setting and relative humidity...  ... then click the calculate button:
 

Additional Information:

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

Example:  at 5050 feet altitude, 95 deg F,  29.45 inches-Hg barometric pressure and 40% relative humidity, the Density Altitude is calculated as 9251 feet.

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 altitude (or elevation) is the geometric altitude above mean sea level where 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:

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

The absolute air 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 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). The standard sea level air density is 1.225 kg/m³ (0.002378 slugs/ft³).

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: 20-Jul-2010