Pressure Altitude Calculator
Pressure altitude is the altitude reading that corresponds to a given atmospheric pressure in the International Standard Atmosphere (ISA), as defined by ICAO Doc 7488 and adopted in the US Standard Atmosphere. This calculator uses the standard troposphere formula: Alt(ft) = (1 - (P/P0)^0.190284) x 145,366.45, where P is the measured pressure in hectopascals (hPa) and P0 = 1,013.25 hPa is the standard sea-level pressure. This formula is used in aviation for altimeter calibration, aircraft performance tables, and flight level computations. Results are shown in both feet and meters.
Pressure altitude formula (ICAO/US Standard Atmosphere)
Alt(ft) = (1 - (P / 1013.25)^0.190284) × 145,366.45
P is atmospheric pressure in hPa (hectopascals = millibars). P0 = 1,013.25 hPa is the standard sea-level pressure (ICAO Doc 7488). The exponent 0.190284 = R g0 / (T0 L) where g0 = 9.80665 m/s^2, R = 287.058 J/(kg K), T0 = 288.15 K, L = 0.0065 K/m. 1 foot = 0.3048 m for conversion.
Standard atmosphere reference points
- Sea level (0 ft): 1,013.25 hPa, 15.00 degrees C
- 5,000 ft (1,524 m): 843.07 hPa, 5.09 degrees C
- 10,000 ft (3,048 m): 696.82 hPa, -4.81 degrees C
- 18,000 ft (5,486 m): 500.00 hPa, -20.73 degrees C (tropopause boundary for many tables)
- 29,029 ft (Mt Everest, 8,849 m): about 314 hPa
Frequently asked questions
What is pressure altitude?
Pressure altitude is the altitude in the International Standard Atmosphere (ISA) that corresponds to a given atmospheric pressure. It is used in aviation for altimeter settings, flight level designations, and aircraft performance calculations.
What formula does this calculator use?
The ICAO/US Standard Atmosphere formula for the troposphere (below about 11,000 m): Alt (ft) = (1 - (P/P0)^0.190284) x 145,366.45, where P is pressure in hPa (mb) and P0 = 1,013.25 hPa. This formula is from the FAA Aeronautical Information Manual and ICAO Standard Atmosphere.
What is the standard sea-level pressure?
The standard sea-level pressure in the International Standard Atmosphere is P0 = 101,325 Pa = 1,013.25 hPa (millibars) = 29.9213 inHg. This is defined by ICAO Doc 7488 and is the reference for pressure altitude calculations.
How is pressure altitude used in aviation?
Aircraft altimeters measure air pressure and convert it to altitude using the standard atmosphere. Pilots set the altimeter to local pressure (QNH) for terrain clearance, or to 29.92 inHg (standard) at or above transition altitude to fly flight levels based on pressure altitude.
What is the difference between pressure altitude and density altitude?
Pressure altitude depends only on pressure. Density altitude adjusts pressure altitude for temperature: DA = PA + 120 x (OAT - ISA temperature at that altitude). High temperature increases density altitude, reducing aircraft performance.
Official sources
- NOAA/NASA: US Standard Atmosphere 1976 (NOAA/NASA).
- FAA: FAA Aeronautical Information Manual.
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.