calculate pressure altitude

Accurately calculate pressure altitude for aviation performance and flight planning.

Standard Atmosphere Reference Table

Altitude (ft)	Standard Pressure (inHg)	Standard Pressure (hPa)	Standard Temp (°C)
0 (Sea Level)	29.92	1013.25	15.0
2,000	27.82	942.1	11.0
5,000	24.90	843.0	5.1
10,000	20.58	696.8	-4.8
18,000	14.94	506.0	-20.7

What is Pressure Altitude?

Pressure altitude is the height above a theoretical plane where the atmospheric pressure is equal to 29.92 inches of mercury (inHg) or 1013.25 hectopascals (hPa). When you calculate pressure altitude, you are essentially determining what your altitude would be if the atmosphere were "standard."

Pilots and engineers use a Pressure Altitude Calculator because aircraft performance—such as takeoff distance, rate of climb, and engine power—is dictated by the density of the air, which is directly related to pressure altitude. It is a critical step before determining density altitude, which further accounts for temperature variations.

Common misconceptions include confusing pressure altitude with indicated altitude. Indicated altitude is what you see on your altimeter when it is set to the local barometric pressure. Pressure altitude is what the altimeter shows when it is set to 29.92 inHg.

Pressure Altitude Calculator Formula and Mathematical Explanation

The mathematical derivation for pressure altitude is based on the standard lapse rate of pressure in the lower atmosphere. For every 1 inch of mercury change in barometric pressure, the altitude changes by approximately 1,000 feet.

The standard formula used by this Pressure Altitude Calculator is:

PA = Elevation + (29.92 – Altimeter Setting) × 1,000

Variables Explanation

Variable	Meaning	Unit	Typical Range
PA	Pressure Altitude	Feet (ft)	-1,000 to 50,000
Elevation	Station/Field Elevation	Feet (ft)	-1,200 to 15,000
Altimeter	Current Barometric Pressure	inHg	28.00 to 31.00
29.92	Standard Sea Level Pressure	inHg	Constant

Practical Examples (Real-World Use Cases)

Example 1: High Pressure Day at Sea Level

Imagine you are at an airport with an elevation of 0 feet (Sea Level). The local altimeter setting is 30.12 inHg. To calculate pressure altitude:

• Elevation: 0
• Altimeter: 30.12
• Calculation: 0 + (29.92 – 30.12) × 1,000 = -200 feet.

In this case, the pressure altitude is actually below sea level because the high pressure makes the air "denser," simulating a lower altitude.

Example 2: Mountainous Airport on a Low Pressure Day

You are at Aspen, Colorado (KASE), which has an elevation of approximately 7,820 feet. The altimeter setting is 29.72 inHg.

• Elevation: 7,820
• Altimeter: 29.72
• Calculation: 7,820 + (29.92 – 29.72) × 1,000 = 7,820 + 200 = 8,020 feet.

The Pressure Altitude Calculator shows that the aircraft will perform as if it were at 8,020 feet in a standard atmosphere.

How to Use This Pressure Altitude Calculator

1. Enter Station Elevation: Input the current elevation of your location or the airport in feet.
2. Enter Altimeter Setting: Input the current barometric pressure provided by ATIS, AWOS, or a local weather station in inches of mercury (inHg).
3. Review Results: The Pressure Altitude Calculator will instantly display the pressure altitude in the highlighted green box.
4. Analyze Intermediate Values: Check the pressure correction and the equivalent hPa value for international flight planning.
5. Interpret the Chart: Use the dynamic chart to see how fluctuations in barometric pressure would impact your pressure altitude.

Key Factors That Affect Pressure Altitude Results

• Barometric Pressure: The most direct factor. As pressure drops, pressure altitude increases.
• Station Elevation: The baseline for the calculation. Higher elevations start with a higher base pressure altitude.
• Standard Atmosphere Assumptions: The formula assumes a standard lapse rate of 1,000 feet per 1 inHg, which is accurate for lower altitudes but varies slightly at extreme heights.
• Weather Systems: High-pressure systems (anticyclones) lower the pressure altitude, while low-pressure systems (cyclones) raise it.
• Instrument Error: If using a mechanical altimeter, friction or calibration errors can lead to incorrect readings before you even calculate pressure altitude.
• Non-Standard Temperature: While temperature doesn't change pressure altitude itself, it drastically affects Density Altitude. Always use the Pressure Altitude Calculator as the first step toward density altitude.

Frequently Asked Questions (FAQ)

1. Why is pressure altitude important for pilots?

It is the baseline for calculating aircraft performance. Engines and wings react to the actual pressure of the air, not the height above the ground.

2. Can pressure altitude be negative?

Yes. If the barometric pressure is higher than 29.92 inHg at sea level, the Pressure Altitude Calculator will return a negative value.

3. Is pressure altitude the same as density altitude?

No. Pressure altitude only accounts for pressure. Density altitude takes pressure altitude and corrects it for non-standard temperature.

4. How often should I calculate pressure altitude?

You should calculate pressure altitude during every pre-flight planning phase, especially when operating at high-elevation airports or in extreme weather.

5. What is the standard pressure in hPa?

The standard sea-level pressure is 1013.25 hPa, which is equivalent to 29.92 inHg.

6. Does humidity affect pressure altitude?

No, humidity affects air density (and thus density altitude), but it does not change the pressure altitude calculation itself.

7. Why do we use 29.92 as the constant?

29.92 inHg is the defined standard sea-level pressure in the International Standard Atmosphere (ISA).

8. How does the 1,000 ft per 1 inHg rule work?

It is a simplified linear approximation of the pressure lapse rate in the troposphere, making it easy to calculate pressure altitude manually if needed.