Are you searching for how to calculate density altitude? Search no more! With this calculator, you can obtain the density altitude by inputting the air temperature, dew point, relative humidity, and the altimeter data. This density altitude is necessary for determining airplane engine performance and lift.
What is density altitude?
Density altitude is a way to express air density in length units (i.e., meters, kilometers, etc.). It is the altitude relative to an International Standard Atmosphere (ISA) model at which the density would equal that at the place of observation. ISA models propose mathematical formulations that describe how atmospheric conditions (pressure, temperature, density, and viscosity) vary according to altitude.
The main application of density altitude is in aviation, where it influences things like:
- Airfoil lift;
- The power delivered by the engine; and
- The relationship between indicated and true airspeed.
This calculator uses the ICAO Standard Atmosphere (ICAO stands for the International Civil Aviation Organization) as the reference model. At zero altitude, this model sets the air temperature to 15 °C (59 °F), air pressure to 1013.25 mbar (29.921 inHg), relative humidity to 0%, and air density to 1.225 kg/m³ (0.076474 lb/ft³).
Now, let's look at the density altitude formula.
How to calculate density altitude?
The formula for density altitude is:
H = 44.3308 - 42.2665 × ρ0.234969
- H — Density altitude, calculated in kilometers (km); and
- ρ — Air density, in kilograms per cubic meter (kg/m³).
To calculate air density (ρ) in aerodynamic applications, we must consider different atmospheric factors, such as air temperature, dew point, relative humidity, and the partial pressures of the dry and moist parts of the air. This density altitude calculator determines that value for you. Still, you can obtain it using our air density calculator (where you can also look at the formulas for its calculation).
And why do we need the altimeter setting and station elevation? Well, when calculating air density, we'll need to know the absolute or total air pressure (the sum of the dry air and vapor pressures), which requires knowing those two parameters:
The altimeter setting is the sea level reference pressure, which pilots settle in the Kollsman window of the altimeter. As this value varies over time, pilots must be aware of its value by checking weather reports. Station elevation is simply the aircraft's elevation, measured by the altimeter. To obtain an accurate elevation measurement, the pilot must correctly settle the altimeter pressure.
Once we know those two values, we can use them in the following equation to obtain the absolute air pressure:
P = (AS0.190263 - 8.417286 × 10-5 × h)1/0.190263
- P — Air pressure, in millibars (mbar);
- AS — Altimeter setting, in mbar; and
- h — Weather station elevation, in meters (m).