Pressure Altitude Calculator
Calculate pressure altitude from altimeter setting and field elevation.
Essential for performance charts, density altitude, and aviation flight planning.
Pressure Altitude
Pressure altitude is the altitude shown by an altimeter when its Kollsman window is set to the standard sea-level pressure of 29.92 inHg (1013.25 hPa). It removes local weather variations from altitude calculations and is the reference altitude used by all aircraft performance charts.
Formula
PA = field elevation + (29.92 − altimeter setting) × 1000 (inHg version)
PA = field elevation + (1013.25 − altimeter setting hPa) × 27.7 (metric version, ft)
Why It Matters
Aircraft engines, propellers, and wings respond to air density, not the geometric altitude. On a low-pressure day, the air at field elevation behaves like a higher altitude. Performance charts (takeoff distance, climb rate, fuel burn) assume standard pressure — so pilots must convert local conditions to pressure altitude before reading the chart.
Worked Example: Denver, Low-Pressure Day
- Field elevation: 5430 ft
- Altimeter setting: 29.55 inHg
- PA = 5430 + (29.92 − 29.55) × 1000 = 5430 + 370 = 5800 ft
The aircraft will perform as if it is at 5800 ft on a standard day, even though it is sitting at 5430 ft.
Pressure Altitude vs Density Altitude
| Concept | What It Captures |
|---|---|
| Pressure altitude | Pressure differences only |
| Density altitude | Pressure + temperature + humidity |
| True altitude | Actual height above mean sea level |
| Indicated altitude | What the altimeter shows with current setting |
For day-of-flight performance, density altitude is the most important — but it is calculated from pressure altitude, which is why this conversion is the first step.
Common Altimeter Settings
| Pressure (inHg / hPa) | Description |
|---|---|
| 29.92 / 1013.25 | Standard atmosphere, PA = field elevation |
| 30.10 / 1019.3 | High-pressure system, PA below field elevation |
| 29.50 / 999.0 | Low-pressure system, PA above field elevation |
| 28.50 / 965.2 | Strong storm, significant performance loss |
Reading the Result
If your pressure altitude is higher than your field elevation, expect reduced performance: longer takeoff rolls, lower climb rates, smaller useful loads. If it is lower, performance improves and the airplane feels eager. The spread between the two values is the pilot’s “weather margin.” The bigger it is, the more important the conversion becomes for safety.
Going further: density altitude
Pressure altitude is the foundation, but day-of-flight performance ultimately depends on density altitude (DA), which folds in temperature:
DA = PA + 120 × (OAT − ISA temp at that altitude)
where ISA temperature at altitude = 15°C − (2°C per 1,000 ft × altitude in thousands of ft), and OAT is the outside air temperature in °C.
A hot summer day at a mountain airport produces a density altitude far higher than the physical elevation. At a 5,000 ft field on a 35°C day, ISA temp is 5°C (15 − 10), so DA = 5,000 + 120 × (35 − 5) = 5,000 + 3,600 = 8,600 ft. The aircraft performs as if it were nearly 9,000 ft up, even though the wheels are at 5,000 ft. Mountain flying accidents disproportionately involve pilots who forgot to convert.
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
SuperGlobalCalculator is independently built and maintained. See how we build and verify our calculators.