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” — and the bigger it is, the more important the conversion becomes for safety.