Pressure Altitude Calculator: Formula and Examples

This pressure altitude calculator estimates altitude in the standard atmosphere from an altimeter setting: enter the indicated pressure altitude or the field elevation and current altimeter setting, and it returns pressure altitude in feet. Pressure altitude is the altitude corresponding to the measured atmospheric pressure, not necessarily your height above the ground.

Formula

For the common aviation approximation, pressure altitude in feet equals field elevation in feet plus (29.92 inches of mercury minus the altimeter setting in inches of mercury) multiplied by 1,000.

• e is the airport or reference-point elevation, in feet.
• a is the local altimeter setting, in inches of mercury (inHg).
• 29.92 inHg is the standard sea-level pressure setting used for pressure altitude (approximately 1013.25 hectopascals, or hPa).
• p is the calculated pressure altitude, in feet. The second output converts it to metres using 1 ft = 0.3048 m.

The calculator uses the familiar approximate rule of 1,000 feet per 1 inHg change. It is intended for practical aviation calculations; the precise relationship between pressure and altitude follows the standard-atmosphere model and is not perfectly linear over all heights.

Worked Example

Using the calculator’s default values, the field elevation is 0 ft and the altimeter setting is 29.92 inHg.

1. Subtract the setting from standard pressure: 29.92 − 29.92 = 0 inHg.
2. Convert that difference to feet: 0 × 1,000 = 0 ft.
3. Add the field elevation: 0 + 0 = 0 ft pressure altitude.
4. Convert to metres: 0 × 0.3048 = 0 m.

For another example, a field at 5,000 ft with a setting of 29.42 inHg gives 5,000 + (29.92 − 29.42) × 1,000 = 5,500 ft pressure altitude. This illustrates the direction of the adjustment: a setting below standard pressure produces a pressure altitude above the field elevation.

What Pressure Altitude Means

Pressure altitude is the altitude in the International Standard Atmosphere (ISA) at which the observed pressure would occur. Pilots and aviation performance calculations use it because aircraft performance depends partly on air density, and pressure is one of the conditions used to characterize that density.

It is different from indicated altitude, true altitude, and density altitude. With the altimeter set to the local pressure setting, the instrument indicates an approximate altitude above mean sea level. With the altimeter set to 29.92 inHg (or 1013.25 hPa), it indicates pressure altitude. True altitude is actual vertical distance above mean sea level; it can differ from indicated altitude because of atmospheric conditions. Density altitude further accounts for temperature and, where applicable, humidity. It is a performance measure, not a direct altimeter setting.

How to Use the Calculator

• Enter the elevation of the airport or location in feet. Use the elevation above mean sea level, not the height of a runway above nearby terrain.
• Enter the current altimeter setting in inHg. Use a setting for the location and time relevant to your calculation.
• Read the first result as pressure altitude in feet. The second result is the same value in metres.

If you already have an altimeter reading while the instrument is set to 29.92 inHg, that reading is pressure altitude; you do not need to apply the field-elevation formula again. In regions or instruments using hectopascals, convert the setting before using this calculator: 1 inHg is approximately 33.864 hPa. The standard setting is approximately 1013.25 hPa.

When It Is Used—and What It Does Not Tell You

Pressure altitude is used as an input to aircraft performance charts and calculations, including takeoff, climb, and engine-performance planning. It also provides a common reference when comparing atmospheric pressure conditions across locations. The result alone does not say whether a particular aircraft can safely operate: performance depends on the aircraft, weight, temperature, runway, wind, configuration, and other conditions. Use the applicable aircraft documentation and operating procedures rather than treating this simple calculation as a go/no-go decision.

Pressure altitude also is not a forecast of an aircraft’s actual height above the ground. It does not include terrain clearance, local temperature effects on true altitude, or the temperature correction used to estimate density altitude. At higher elevations or where accuracy matters, use the relevant standard-atmosphere equations or approved aviation tools rather than assuming the 1,000-ft-per-inHg rule is exact.

Common Errors and Limits

• Reversing the pressure difference: The adjustment is 29.92 minus the setting. A lower-than-standard setting raises calculated pressure altitude; a higher setting lowers it.
• Mixing units: The formula’s 29.92 is in inHg. Do not enter an hPa value in that field. Convert units first, or use a formula expressed entirely in hPa.
• Using the wrong elevation: Enter elevation in feet, not metres, and make sure it refers to the same location as the pressure setting.
• Expecting exactness from the rule of thumb: The 1,000-ft-per-inHg factor is a practical approximation. Rounding the setting or elevation can also shift the displayed result.

Settings may be reported to different precision, and weather changes over time and distance. For operational use, follow the relevant aviation procedures and use current, location-appropriate data. This calculator is a conversion aid, not a substitute for flight planning or instrument procedures.

Frequently Asked Questions

How do I calculate pressure altitude from field elevation?
Use: pressure altitude (ft) = field elevation (ft) + (29.92 − altimeter setting in inHg) × 1,000. The setting must be in inches of mercury for this form of the formula.

What happens when the altimeter setting is below 29.92?
The calculated pressure altitude is higher than the field elevation, because the pressure setting is below standard sea-level pressure. A setting above 29.92 produces a lower calculated pressure altitude.

Is pressure altitude the same as density altitude?
No. Pressure altitude reflects pressure relative to the standard atmosphere. Density altitude also accounts for air temperature and is used to describe the altitude in the standard atmosphere with equivalent air density.

Can I calculate pressure altitude with an altimeter?
Yes. Set a barometric altimeter to 29.92 inHg, or 1013.25 hPa, and its indicated altitude is pressure altitude, subject to instrument accuracy and operating procedures.

How do I convert pressure altitude from feet to metres?
Multiply feet by 0.3048. For example, 5,500 ft is 1,676.4 m; a rounded calculator display may show 1,676 m.

Related

• Calculating Energy: Formula, Units, and Examples
• Calculate Wavelength From a Calibration Curve
• Aquarium Force Calculator: Pressure on the Glass

in e | Field elevation | ft | 0 | 0
in a | Altimeter setting | inHg | 29.92 | 0
out p | Pressure altitude | ft | e + (29.92 - a) * 1000 | 0
out m | Pressure altitude | m | p * 0.3048 | 0