Pressure Altitude Calculator

Formula Used

Pressure altitude is the altitude in a standard atmosphere that corresponds to a measured static pressure. This calculator uses the International Standard Atmosphere (ISA) pressure–height relationships.

Constants: T₀ = 288.15 K, L = 0.0065 K/m, g₀ = 9.80665 m/s², R = 287.05287 J/(kg·K), h₁₁ = 11000 m, T₁₁ = 216.65 K.

How to Use This Calculator

1. Enter the measured static (station) pressure.
2. Select the pressure unit that matches your instrument or dataset.
3. Choose a sea‑level reference: standard or a custom reference value.
4. Select your preferred output unit for the altitude.
5. Click Calculate to display results above the form.
6. Use the download buttons to export the current result.

Example Data Table

Sample values below illustrate how pressure maps to pressure altitude under a standard reference.

Table altitudes are rounded, for illustration only.

Pressure Altitude: Practical Notes

Engineers, pilots, and researchers use pressure altitude to standardize pressure readings. This section summarizes interpretation, assumptions, and quick checks so outputs remain consistent.

1) What pressure altitude represents

Pressure altitude is the height in a standard atmosphere that would produce the same static pressure you measured. It is a pressure-to-height conversion, not a geometric height. Because it depends on pressure alone, it is widely used to compare conditions across locations.

2) Standard atmosphere model behind the calculation

The calculator uses the ISA profile: sea-level temperature 288.15 K with a 6.5 K per kilometer lapse rate up to 11 km, then an isothermal layer. This piecewise model provides a consistent operational reference for pressure-height conversion.

3) Why the sea-level reference pressure matters

Using standard sea-level pressure (1013.25 hPa) yields the conventional pressure altitude. A custom reference can help controlled comparisons, such as normalizing two datasets to the same baseline. Small reference shifts can move the computed altitude by hundreds of feet.

4) Aviation interpretation and flight levels

When altimeters are set to 1013.25 hPa, indicated altitude approximates pressure altitude and is expressed as a flight level (hundreds of feet). This calculator reports an approximate FL from the computed feet value. Always follow published procedures and ATC instructions.

5) Relationship to air density and performance

Pressure altitude is a key ingredient for density altitude, which also depends on temperature and humidity. Higher pressure altitude generally implies lower air density, reducing lift and engine performance. For performance planning, combine pressure altitude with ambient temperature rather than using it alone.

6) Measurement quality and common pitfalls

Use station or static pressure, not sea-level-reduced pressure from weather products unless you intend that interpretation. Ensure the sensor is vented and calibrated, and avoid transient readings near exhaust or prop wash. Even a few hPa of error can shift altitude noticeably.

7) Typical pressure ranges and sanity checks

Near sea level, pressures around 1013 hPa correspond to roughly 0 ft pressure altitude. Around 900 hPa is commonly a few thousand feet, and 700 hPa is near ten thousand feet. The example table shows rounded values to help catch unit mistakes quickly.

8) Limits and best practices

ISA is an approximation, so local weather can shift the true geometric height for a given pressure. Treat the output as a standard-atmosphere equivalent. Keep units consistent, prefer direct sensor pressure, and export results to document calculations in reports.

FAQs

1) Is pressure altitude the same as altitude above sea level?

No. Pressure altitude is the standard-atmosphere height that matches your measured pressure. True elevation depends on local temperature structure and weather systems, so it can differ from the pressure-based value.

2) How is pressure altitude different from density altitude?

Density altitude adjusts pressure altitude using temperature (and sometimes humidity). It reflects air density and performance effects. Pressure altitude uses pressure only and is mainly a standardized reference.

3) Which pressure should I enter for aviation use?

Enter static or station pressure when available. If you only have altimeter setting, convert carefully or use a method consistent with your procedure. Avoid mixing sea-level-reduced pressure with station pressure unintentionally.

4) Can the result be negative?

Yes. If the measured pressure is higher than the reference sea-level pressure, the standard-atmosphere equivalent height becomes negative. This can occur in strong high-pressure conditions or at very low elevations.

5) Why offer a custom sea-level reference pressure?

Custom reference lets you normalize results to a chosen baseline for analysis, testing, or comparisons across datasets. Standard reference is preferred for conventional pressure altitude and flight-level interpretation.

6) What range does the calculator support?

The implementation covers the ISA troposphere and the lower stratosphere model segment. Extremely low pressures outside typical operational ranges may produce unreliable results, so keep inputs within realistic atmospheric values.

7) Why doesn’t it match GPS altitude?

GPS reports geometric height relative to a reference ellipsoid or geoid model. Pressure altitude is derived from pressure using a standard atmosphere. Different definitions and changing weather conditions naturally create differences.