Density Altitude Lab

Methodology & formula citations

Every number on this page comes from a published, citable formula. No black boxes.

• Density altitude (dry): DA = PA + 120 × (OAT − T_ISA), with T_ISA = 15 − 0.0019812 × PA(ft) °C. Source: FAA Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25), weather-theory chapter (public domain).
• Humidity correction: outside air temperature is replaced by virtual temperature T_v = T / (1 − (e/p)(1 − 0.622)), where vapor pressure e comes from the Magnus formula e = 6.1094·exp(17.625·T/(243.04+T)) hPa. Source: Alduchov & Eskridge (1996), J. Applied Meteorology; virtual temperature is the standard meteorological definition. Pressure p at pressure altitude comes from the ISA below.
• Pressure altitude: PA = elevation + (29.92 − QNH_inHg) × 1000 ft; equivalently PA = 145366.45 × (1 − (p/1013.25)^0.190284) ft from absolute pressure. Standard altimetry (set 29.92 in the Kollsman window).
• ISA model: ICAO / U.S. Standard Atmosphere 1976 — sea level 15 °C / 1013.25 hPa / 1.225 kg/m³, lapse 6.5 °C/km to 11 km, isothermal to 20 km; density ρ = p/(R·T), R = 287.05 J/(kg·K).
• TAS / Mach: compressible isentropic relations: q_c = p₀[(1+0.2M²)^3.5−1]; M = √{5[(q_c/p+1)^2/7−1]}; a = a₀√(T/288.15). Source: NASA Glenn Research Center, compressible flow relations.
• Performance: Koch-chart linear approximations per Embree, Axioms of Flight (Flight Information Publications, 1984); anchor worked example (100 °F, 6,000 ft PA → +230% takeoff, −76% climb) per the FAA Koch chart (AC 90-14, public domain).

Frequently asked questions