Density Altitude Calculator

About the Density Altitude Calculator

Density altitude is the altitude at which the air density equals the current local density. High density altitude (hot, high, humid) reduces aircraft and engine performance.

Enter the pressure altitude (ft) and outside air temperature (°C). The tool uses the standard approximation DA = PA + 120 × (OAT − ISA temp), where ISA temp = 15 − 1.98 × (PA/1000) °C.

How to use this calculator

1. Enter the pressure altitude, which is the altitude corrected for local pressure.
2. Enter the outside air temperature in degrees, usually in \(^{\circ}\text{C}\).
3. Use the calculator to compare the actual temperature with the standard atmosphere temperature at that altitude.
4. Read the density altitude result to judge performance, since a higher density altitude means thinner air.

The formula explained

The formula \(DA = PA + 120\,(T - T_{ISA})\) estimates density altitude from pressure altitude and the difference between actual temperature and standard temperature. It shows how much the air behaves like it is higher or lower than the pressure altitude.

• DA = density altitude
• PA = pressure altitude
• T = outside air temperature
• \(T_{ISA}\) = standard temperature from the International Standard Atmosphere at that altitude

Step by step method

1. Start with the pressure altitude \(PA\).
2. Find the temperature difference \(T - T_{ISA}\).
3. Multiply that difference by \(120\).
4. Add the result to \(PA\) to get \(DA\).

Worked example

Problem. An airport has a pressure altitude of \(5{,}000\) ft and an outside air temperature of \(30{}^{\circ}\text{C}\). If the ISA temperature at that altitude is \(5{}^{\circ}\text{C}\), what is the density altitude?

1. Compute the temperature difference: \(30 - 5 = 25{}^{\circ}\text{C}\).
2. Multiply by \(120\): \(120 \times 25 = 3{,}000\) ft.
3. Add to the pressure altitude: \(5{,}000 + 3{,}000 = 8{,}000\) ft.

Tips and common mistakes

• Make sure the temperature difference uses the ISA temperature at the same altitude, not sea level.
• A hotter day gives a higher density altitude, which usually means worse aircraft performance.

Frequently asked questions