✈️ Pressure Altitude Converter
Convert atmospheric pressure to pressure altitude using the International Standard Atmosphere (ISA) model. Enter any pressure value (hPa, inHg, mmHg, kPa, atm, or PSI) and get the corresponding altitude in meters and feet, along with the standard temperature and pressure ratio.
What Is Pressure Altitude?
Pressure altitude is the altitude in the International Standard Atmosphere (ISA) at which the atmospheric pressure equals a given pressure value. In other words, it is the altitude that corresponds to a specific pressure reading when standard atmospheric conditions are assumed.
Pressure altitude is a fundamental concept in aviation, meteorology, and engineering. It is used to standardize aircraft performance calculations, altimeter settings, and weather analysis.
What Is the International Standard Atmosphere (ISA)?
The International Standard Atmosphere (ISA) is a static atmospheric model that defines how pressure, temperature, density, and viscosity change with altitude. Key assumptions:
- Sea-level pressure: 1013.25 hPa (29.92 inHg)
- Sea-level temperature: 15 °C (288.15 K)
- Temperature lapse rate: −6.5 °C per km (up to 11 km)
- Tropopause altitude: 11,000 m (36,089 ft)
- Stratosphere temperature: −56.5 °C (constant above 11 km)
How to Calculate Pressure Altitude
For the troposphere (0 to 11,000 m), the ISA formula is:
For the stratosphere (above 11,000 m), the formula is:
For example, at standard sea-level pressure of 1013.25 hPa:
h = 44330.77 × [1 − (1013.25 / 1013.25)0.190263]
h = 44330.77 × [1 − 1]
h = 0 m (sea level)
At a pressure of 500 hPa (approximately 5,500 m):
h = 44330.77 × [1 − (500 / 1013.25)0.190263]
h ≈ 44330.77 × [1 − 0.8846]
h ≈ 5,116 m (≈ 16,785 ft)
Why Use This Converter?
- Multiple pressure units: Enter pressure in hPa, inHg, mmHg, kPa, atm, or PSI.
- Multiple altitude units: Get results in meters or feet.
- Step-by-step breakdown: See the exact calculation and formulas used.
- ISA table reference: Compare your result with standard atmosphere values.
- Free & private: No registration, no data storage — all calculations are done in your browser.
❓ Pressure Altitude Converter FAQ
What is pressure altitude?
Pressure altitude is the altitude in the International Standard Atmosphere (ISA) where the pressure equals a given value. It is used to standardize aircraft performance calculations and altimeter settings.
What is the standard sea-level pressure?
Standard sea-level pressure in the ISA is 1013.25 hPa, which is equivalent to 29.92 inHg, 760 mmHg, 101.325 kPa, or 1 atm.
What is the ISA temperature lapse rate?
The ISA temperature lapse rate in the troposphere is −6.5 °C per kilometer (−1.98 °C per 1,000 ft) up to 11,000 m.
What happens above 11,000 meters?
Above 11,000 m (the tropopause), the ISA assumes a constant temperature of −56.5 °C (216.65 K). This is the isothermal layer of the stratosphere. The pressure-altitude formula changes accordingly.
How do I convert inHg to hPa?
1 inHg = 33.8639 hPa. To convert inHg to hPa, multiply by 33.8639. To convert hPa to inHg, divide by 33.8639.
How do I convert mmHg to hPa?
1 mmHg = 1.33322 hPa (also known as 1 Torr). To convert mmHg to hPa, multiply by 1.33322.
How do I convert PSI to hPa?
1 psi = 68.9476 hPa. To convert PSI to hPa, multiply by 68.9476.
What is the difference between pressure altitude and true altitude?
Pressure altitude is based on the standard atmosphere model. True altitude is the actual height above mean sea level. The difference depends on the local altimeter setting and temperature.
How accurate is this converter?
This converter uses the exact ISA formulas defined by ICAO and the U.S. Standard Atmosphere 1976. Results are accurate to within a few meters for pressures within the ISA range.
Is this converter free?
Yes, this converter is completely free to use. No registration or personal data storage is required.