Introduction
Pressure altitude is the altitude an altimeter shows when it is set to 29.92 inHg: the height above the standard datum plane, where the pressure is 29.92 inHg.2 It is the basis for aircraft performance data and for the flight levels flown above 18,000 feet.1 It matters because air pressure changes with weather and location, so the atmosphere rarely matches "standard" conditions.
This pressure altitude calculator helps you find pressure altitude in three ways. The Quick Station Pressure Calculator takes a raw station pressure reading and gives you the pressure altitude in feet or meters. The Elevation + Altimeter Setting Calculator uses your airport elevation and the current altimeter setting to find pressure altitude. The Advanced ISA Atmosphere Calculator lets you work with the full International Standard Atmosphere (ISA) model, convert between pressure and altitude, adjust baseline conditions, and see step-by-step math for each result.
Each module shows a detailed, worked solution so you can follow the math and learn how the formulas work. A built-in reference table lists standard pressures at common altitudes from below sea level up to 65,000 feet.
How to Use Our Pressure Altitude Calculator
Enter your pressure or altitude readings into any of the three calculator modules below. The tool will instantly calculate the pressure altitude and show you a full step-by-step solution.
Preferred Altitude Unit
Pick Feet or Meters at the top of the page. This choice applies to all three calculators at once and sets your default altitude unit everywhere.
Quick Station Pressure Calculator
Type your station pressure into the input field. This is the raw, uncorrected pressure reading from your barometer or weather station, not the altimeter setting.
Select the pressure unit that matches your reading: inHg, mmHg, or mbar/hPa. The calculator will convert between units automatically.
Click Calculate Pressure Altitude to see your result in both feet and meters, along with the full worked solution.
Elevation + Altimeter Setting Calculator
Enter your airport or field elevation in the first box. You can use negative values for locations below sea level, like Death Valley.
Choose Feet or Meters for your elevation unit. The calculator will convert your value if you switch units.
Type the current altimeter setting (barometric pressure corrected to sea level) in the second box. The standard value is 29.92 inHg (1013.2 mbar).1
Select inHg or Millibars for the altimeter setting unit.
Click Calculate to get the pressure altitude for your airport or location.
Advanced ISA Atmosphere Calculator
Choose a calculation direction. Pick Pressure → Altitude to find altitude from a pressure reading, or Altitude → Pressure to find the air pressure at a given altitude.
Enter the sea level pressure baseline. The default is the ISA standard value of 101,325 Pa.4 Pick your preferred unit from the dropdown: Pa, psi, atm, inHg, or mbar/hPa.
Enter the sea level temperature baseline. The ISA default is 15 °C.1 Choose °C, °F, or K to match your value.
Type your air pressure or altitude in the main input field, depending on which direction you chose. Then pick the matching unit from the dropdown next to it.
Select your preferred output unit from the dropdown on the right side. This controls whether your result shows in feet, meters, or a specific pressure unit.
Click Calculate to see the result, the atmospheric layer (Troposphere or Stratosphere), the ISA deviation, and a full step-by-step breakdown with a pressure–altitude chart.
Altitude–Pressure Reference Table
Scroll down to the reference table to view standard atmosphere pressure values at altitudes from −5,000 ft to 65,000 ft. No input is needed. This table uses ISA standard conditions and is color-coded by atmospheric layer.
What Is Pressure Altitude?
Pressure altitude is the height above the standard datum plane, the level where the air pressure is 29.92 inHg. An altimeter is a barometer calibrated to the standard atmosphere, so with 29.92 set in it, it shows the altitude in the standard atmosphere that matches the pressure it senses.1 Pilots use it to know how their aircraft will perform during takeoff, landing, and flight.
Why Pressure Altitude Matters
Air pressure changes with weather and location, so the same runway can have a different pressure altitude from one hour to the next. Lower pressure means thinner air, and thin air reduces engine power, propeller thrust, and wing lift.1 Aircraft performance charts are built on the standard atmosphere, which is why they are entered with pressure altitude. Corrected for nonstandard temperature, pressure altitude becomes density altitude, the altitude the aircraft actually performs at.1
How Pressure Altitude Is Calculated
There are two common ways to find pressure altitude:
- From station pressure: Find the altitude in the standard atmosphere that has that pressure. Near the ground, pressure falls about 1 inHg for every 1,000 feet, but the standard atmosphere puts 20.57 inHg at 10,000 feet.1 A straight "1,000 feet per inch" rule would call that 9,350 feet, so this calculator uses the full standard-atmosphere formula.
- From field elevation and altimeter setting: Start with the airport elevation, then add the altimeter-setting correction. The correction is the standard-atmosphere altitude of the altimeter setting: 29.7 inHg adds 205 feet, 28.0 inHg adds 1,824 feet, and 30.0 inHg subtracts 73 feet.1
Station pressure is the raw air pressure measured right at the instrument. It is not the same as the altimeter setting, which has already been adjusted to sea level.
The Standard Atmosphere (ISA)
Aviation uses a model called the International Standard Atmosphere (ISA). It assumes sea-level pressure is 29.92 inHg (1013.2 hPa) and the temperature is 15 °C (59 °F).1 It also assumes the temperature drops by about 2 °C for every 1,000 feet gained.1 The tropopause is at 36,089 feet, and above it, in the lower stratosphere, the temperature stays constant at −56.5 °C.3 These standard values give pilots and engineers a shared baseline to compare real conditions against. The ISA model is grounded in the same gas behavior described by the ideal gas law, which relates pressure, temperature, and volume in the atmosphere.
When Pilots Use Pressure Altitude
Pilots check pressure altitude before every flight. They use it to look up takeoff and landing distances, climb rates, and engine performance in their aircraft manuals. Above 18,000 feet, aircraft fly flight levels based on pressure altitude.1 Any time the actual air pressure differs from the standard, pilots must account for the change. Ignoring it can lead to dangerously long takeoff rolls or reduced climb ability, especially at high-elevation airports or on hot days.