Density & Pressure Altitude Calculator
Enter field elevation and QNH (1013.25 hPa ISA), or pressure altitude directly. OAT in °C or °F. ISA lapse rate: 15 °C at MSL, −2 °C per 1,000 ft.
Γëê 609.6 m AMSL
Formula: Pressure Alt = Elev + (1013.25 − QNH) × 30 ft · Density Alt = PA + 120 × (OAT − ISA temp). ISA temp = 15 − 2 × (PA / 1000) °C.
Results
How it works
Pressure altitude
When you set your altimeter to 1013.25 hPa (29.92 inHg), the reading is pressure altitude. From field elevation, we derive it as: elevation + (1013.25 − QNH) × 30 ft per hPa.
ISA standard atmosphere
At mean sea level under ISA, temperature is 15 ┬░C at 1013.25 hPa. Temperature decreases 2 ┬░C for every 1,000 ft of pressure altitude ΓÇö not every 100 ft. At 5,000 ft PA, ISA temp is 5 ┬░C.
Density altitude
Hot air is less dense, so aircraft perform as if they are at a higher altitude. The rule-of-thumb used by pilots and CASA training materials: add 120 ft to pressure altitude for every 1 ┬░C that OAT exceeds ISA at that level.
