Pressure Altitude (Weather) Calculator
Pressure altitude is the height above the standard datum plane, the altitude an altimeter shows when set to the standard sea-level pressure of 29.92 inches of mercury. Pilots use it as the foundation for aircraft performance and density altitude calculations. This calculator takes your field elevation in feet and the current altimeter setting in inches of mercury, then applies the standard 1,000 feet per inch correction to return pressure altitude. Lower altimeter settings push pressure altitude above field elevation; higher settings pull it below.
Pressure altitude formula
Correction = (29.92 - altimeter setting) * 1,000
Pressure altitude = field elevation + correction
Standard pressure datum = 29.92 inches Hg = 1013.25 hPa
Approximation: 1 inch Hg per 1,000 ft near sea level
This is the standard aviation linear approximation. For high precision, performance computers use the full International Standard Atmosphere; near typical airfield elevations the difference is small.
Pressure altitude context
- The standard sea-level pressure datum is 29.92 inches Hg (1013.25 hPa).
- Each 0.01 inch Hg of altimeter setting equals about 10 feet of pressure altitude.
- An altimeter setting below standard makes pressure altitude exceed field elevation.
- Pressure altitude is the input to density altitude once temperature is included.
- US flight levels (at and above 18,000 ft) are flown on the standard 29.92 setting.
Pressure altitude: frequently asked questions
What is pressure altitude?
Pressure altitude is the altitude indicated when an altimeter is set to the standard sea-level pressure of 29.92 inches of mercury (1013.25 hPa). It is the height above the standard datum plane and is used for aircraft performance calculations and high-altitude flight levels.
How do I calculate pressure altitude?
Pressure altitude equals the field elevation plus a correction of (29.92 minus the altimeter setting) times 1,000 feet per inch of mercury. When the altimeter setting is below 29.92, pressure altitude is higher than the field elevation; when it is above, pressure altitude is lower.
Where does the 1,000 feet per inch figure come from?
Near sea level in the International Standard Atmosphere, pressure falls by about 1 inch of mercury per 1,000 feet of altitude. Aviation uses this linear approximation, so each 0.01 inch Hg of altimeter setting difference corresponds to about 10 feet of pressure altitude.
What is the altimeter setting?
The altimeter setting is the local station pressure reduced to sea level, reported in inches of mercury at US airfields (for example 30.12). Pilots dial it into the altimeter so it reads true field elevation on the ground. The standard value is 29.92 inches Hg.
Why does pressure altitude matter for aircraft?
Aircraft engine and aerodynamic performance depend on air density, which is governed by pressure and temperature. Pressure altitude is the first step toward density altitude. It is also the reference for flight levels at and above 18,000 feet in US airspace.
Official sources
- Federal Aviation Administration: Federal Aviation Administration.
- NOAA National Weather Service: National Weather Service.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.