How to Calculate Density Altitude

Step 1 — Pressure Altitude (PA)

This step measures how far today's pressure sits from the standard 29.92 inches of mercury, converts that difference into feet, and moves the field elevation by that amount. The result is the altitude the atmosphere's pressure says the airport is at today.

General formula

Pressure Altitude (PA) = Field Elevation (FE) + (29.92 − Altimeter Setting (AS)) × 1,000

Every 0.01 inches of mercury = 10 feet. A setting above 29.92 pushes PA below field elevation, and vice versa.

Step 2 — Standard Temperature (International Standard Atmosphere, ISA)

On a standard day the air is 15 °C at sea level and cools about 2 °C for every 1,000 feet of climb. This step finds what the temperature would be at your pressure altitude on that standard day, which becomes the baseline for the final step.

General formula

Standard Temperature (ISA Temp) = 15 − 2 × (Pressure Altitude (PA) ÷ 1,000)

15 °C at sea level, cooling 2 °C per 1,000 feet.

Step 3 — Density Altitude (DA)

This step compares the actual temperature with that standard baseline. Every degree warmer than standard thins the air enough to add about 120 feet of apparent altitude, so the difference is multiplied by 120 and added to pressure altitude. The result is the altitude the airplane thinks it is at.

General formula

Density Altitude (DA) = Pressure Altitude (PA) + 120 × (Outside Air Temp (OAT) − Standard Temperature (ISA Temp))

120 feet per °C above standard; subtract 120 per degree below it.

Density Altitude Chart

How to read it

Enter at the bottom at your outside air temperature and rise to your pressure-altitude diagonal (the red dashed diagonal is your exact PA, interpolated between the printed lines).
From that intersection, read straight across to the left axis. That is your density altitude. The two solid marker lines trace this exact path.
The steep dashed line is standard temperature (ISA): whenever your point sits right of it, the air is warmer than standard and DA exceeds PA.

The chart is drawn from the same 120 ft/°C rule as the steps above, so the graphical answer and the arithmetic always agree. The printed FAA chart uses the full standard-atmosphere model and can differ by roughly 100–200 feet. But on test day, work the printed chart as procedure, then let the mental math confirm it.
Everything on this page assumes dry air. On humid days (dew point 20 °C or higher), true density altitude runs a few hundred feet higher than any dry-air method shows.