Find the current pressure altitude
Find the current outside air temperature
Use a density altitude chart or E6B/flight computer with pressure altitude and temperature
Apply the density altitude formula if needed: Density Altitude = Pressure Altitude + [120 × (OAT − ISA temperature at that altitude)]
Determine ISA temperature at the altitude: 15°C at sea level, decreasing about 2°C per 1,000 feet
Subtract ISA temperature from outside air temperature
Multiply the temperature difference by 120
Add the result to the pressure altitude
Use the final value as the density altitude