Pressure Altitude Calculator
Calculate pressure altitude from field elevation and altimeter setting/QNH with aviation and metric pressure units.
Calculator is for informational purposes only. Verify operational calculations with current official weather information and approved aircraft data. Terms and Conditions
Here, h is field elevation in feet and A is altimeter setting/QNH in inHg. This FAA-style formula is the default; Advanced Options also includes an NWS standard-atmosphere calculation.
Enter field elevation and altimeter setting
Use the published field elevation and the current altimeter setting/QNH, not raw station pressure.
The example uses a 5,000 ft field elevation and 29.72 inHg altimeter setting. Valid results update automatically.
Pressure Altitude Result
The primary answer is followed by the pressure correction, pressure comparison, and calculation steps.
Result details
- Pressure correction—
Show calculation steps Review conversions, pressure correction, substitution, and result checks
- Enter valid values to see the complete calculation.
Method, Sources, and Assumptions
Calculation basis, constants, limitations, and authoritative aviation references.
Pressure altitude is the altitude indicated with the altimeter set to 29.92 inHg. The default calculation uses the familiar FAA aviation approximation based on field elevation and altimeter setting/QNH.
- Enter altimeter setting/QNH rather than uncorrected station pressure in the main pressure field.
- The FAA aviation formula is an approximation based on about 1,000 ft of altitude per 1 inHg pressure-setting difference.
- Pressure altitude alone does not account for temperature; use density altitude when temperature effects on aircraft performance are needed.
- Verify operational decisions with current official weather data and the applicable POH/AFM or operating procedures.
Calculator guide
What Pressure Altitude Means
Pressure altitude is the altitude an altimeter indicates when referenced to the standard pressure setting of 29.92 inHg. The calculator above uses two primary inputs—field elevation and altimeter setting/QNH—and returns pressure altitude in feet or meters, plus the pressure correction relative to the field elevation.
In practical terms, pressure altitude places the current pressure on a standard-atmosphere altitude scale. A lower-than-standard altimeter setting makes pressure altitude higher than field elevation; a higher-than-standard setting makes it lower. Temperature is not part of the basic pressure-altitude calculation, so pressure altitude should not be confused with density altitude.
- Primary inputs
- Field elevation and altimeter setting/QNH
- Primary output
- Pressure altitude in feet or meters
- Standard reference
- 29.92 inHg / 1013.25 hPa (conventional standard references)
How to Use the Calculator
The shortest path to a valid result is to enter the published field elevation and the current reported altimeter setting/QNH, then confirm the units. The calculator updates automatically.
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Enter the field elevation
Use the published airport or site elevation. The calculator accepts feet or meters and also allows negative elevations for locations below mean sea level.
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Enter the altimeter setting or QNH
Use the current reported altimeter setting from an official aviation weather source such as METAR, ATIS, AWOS, or ASOS. Select inHg, hPa, or mbar to match the report.
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Read the pressure altitude and correction
The result card shows pressure altitude, the correction relative to field elevation, whether pressure is above or below the standard reference, and the calculation steps.
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Use Advanced Options only when needed
The default is the familiar aviation approximation. Advanced Options lets you switch to the NWS standard-atmosphere method and choose feet or meters for the answer.
Pressure Altitude Formula and Method
For the default calculator mode, pressure altitude is estimated by adding a pressure-setting correction to field elevation. The correction is based on how far the altimeter setting is from the standard 29.92 inHg reference.
Aviation approximation
Plain language: pressure altitude equals field elevation plus the difference between 29.92 inHg and the current altimeter setting, multiplied by approximately 1,000 feet per inch of mercury.
This is an aviation approximation, not an exact linear law of the atmosphere. It is useful because it matches the familiar pilot workflow and makes the direction and approximate size of the pressure correction easy to check.
- \(PA\)
- Pressure altitude Altitude on the standard-atmosphere pressure scale.
- \(h\)
- Field elevation Published airport or site elevation used as the reference elevation.
- \(A\)
- Altimeter setting / QNH The sea-level-referenced pressure setting used to set the altimeter.
How to find pressure altitude without a calculator
In an aircraft, pressure altitude can be obtained directly by setting the altimeter to 29.92 inHg and reading the indicated altitude. That is the defining aviation reference for pressure altitude. The equation above is a convenient way to estimate the same quantity from field elevation and the current altimeter setting when you are not reading it directly from an altimeter.
Worked Pressure Altitude Example
Use the calculator’s loaded example: a field elevation of 5,000 ft and an altimeter setting of 29.72 inHg. This is a useful example because the pressure differs from standard enough to produce a visible correction.
Find the pressure correction
Add the correction to field elevation
Result
Pressure altitude = 5,200 ft
Because 29.72 inHg is below the 29.92 inHg reference, the pressure altitude is 200 ft above the field elevation.
How to Interpret Pressure Altitude
The result tells you which altitude in the standard atmosphere corresponds to the current pressure condition. The difference from field elevation is the quickest way to understand what the pressure is doing to the result.
Lower pressure raises pressure altitude
Holding field elevation constant, an altimeter setting below 29.92 inHg gives a positive correction. For the default approximation, each 0.10 inHg below standard adds about 100 ft.
Higher pressure lowers pressure altitude
Holding field elevation constant, an altimeter setting above 29.92 inHg gives a negative correction. A 30.22 inHg setting is 0.30 inHg above standard, so the approximate correction is −300 ft.
At standard pressure, the correction is zero
With the default formula and an altimeter setting of 29.92 inHg, pressure altitude equals field elevation because the pressure-setting difference is zero.
| Altimeter setting (inHg) | Approx. correction to field elevation (ft) |
|---|---|
| 28.92 | +1,000 |
| 29.42 | +500 |
| 29.72 | +200 |
| 29.92 | 0 |
| 30.12 | −200 |
| 30.42 | −500 |
| 30.92 | −1,000 |
Pressure altitude vs other altitude terms
| Altitude type | Reference | What it means |
|---|---|---|
| Indicated altitude | Current altimeter setting | The altitude displayed by the altimeter with the selected pressure setting. |
| Pressure altitude | 29.92 inHg standard reference | The standard-atmosphere altitude corresponding to pressure. |
| Density altitude | Air density | Pressure altitude corrected for nonstandard temperature. |
| True altitude | Mean sea level | The actual vertical distance above mean sea level. |
| Absolute altitude | Terrain | Height above the surface or terrain, commonly expressed as AGL. |
Pressure Altitude vs Density Altitude
Pressure altitude is a standardized pressure reference. Density altitude starts with pressure altitude and corrects it for nonstandard temperature, making it more directly useful for evaluating how air density affects aircraft performance. If temperature is significantly above or below standard, pressure altitude and density altitude can differ substantially.
Altimeter Setting, QNH, and Input Quality
The calculation is simple enough that input quality is usually the biggest source of a wrong answer. The most important distinction is between altimeter setting/QNH and uncorrected station pressure.
- Altimeter setting / QNH
- A sea-level-referenced pressure setting used so an altimeter on the ground indicates the airport’s elevation. This is the pressure input expected by the calculator above.
- Station pressure
- The actual atmospheric pressure at the station elevation. The NWS direct pressure-altitude equation uses station pressure, so raw station pressure should not be entered into the calculator’s altimeter-setting field.
- inHg
- Inches of mercury, commonly used for U.S. aviation altimeter settings. A METAR group such as
A2992corresponds to 29.92 inHg. - hPa / mbar
- Hectopascals and millibars are numerically equivalent for this purpose. A QNH report such as
Q1013represents 1013 hPa.
A useful metric mental check is that a 1 hPa change corresponds to roughly 30 ft of pressure-altitude correction in the common approximation. This is only a quick check, not a replacement for the calculator or approved performance procedures.
- Match the pressure unit selector to the source before evaluating the result; entering 1013 while the field is still set to inHg will be rejected as unrealistic.
- Use a current observation. Pressure changes with weather, so an old altimeter setting can produce a mathematically correct result for the wrong time.
- Confirm that the elevation is the intended field or site elevation and that feet/meters are selected correctly.
- If another calculator asks for station pressure rather than QNH, do not expect the same input workflow even though the final quantity is also pressure altitude.
Aviation Approximation vs Standard-Atmosphere Method
The calculator provides two methods because the familiar aviation correction is intentionally simple, while the standard-atmosphere relationship is nonlinear. Both are useful, but they answer the same pressure-altitude question with different levels of mathematical detail.
Aviation approximation
This is the default mode. It uses field elevation plus approximately 1,000 ft for each 1.00 inHg that the altimeter setting is below 29.92, or subtracts the corresponding amount when pressure is above standard. It is transparent, fast to check mentally, and matches the familiar pilot calculation.
NWS standard-atmosphere method
This advanced mode first derives station pressure from the entered field elevation and altimeter setting, then applies the NWS pressure-altitude equation. Because atmospheric pressure does not vary linearly with altitude, this method can differ slightly from the 1,000 ft/inHg approximation.
NWS pressure-altitude relationship
Here, \(P_{stn}\) is station pressure in hPa or millibars, and the resulting pressure altitude is in feet.
Assumptions and Limits
Pressure altitude is a standardized pressure reference. The calculator can determine that reference from the entered elevation and pressure setting, but it cannot determine all of the conditions that govern actual aircraft performance or altimetry accuracy.
The default method is approximate
The 1,000 ft/inHg correction treats the pressure-setting relationship as linear for a convenient aviation estimate. The Advanced NWS method is available when you want the standard-atmosphere relationship used by the calculator.
Temperature is intentionally not an input
Temperature is not required to calculate basic pressure altitude from field elevation and altimeter setting. Temperature becomes important when determining density altitude and aircraft performance in nonstandard conditions.
The tool does not validate the weather source
The calculator can check whether an entered pressure is numerically plausible, but it cannot confirm that the observation is current, local to the intended airport, or operationally appropriate.
The result is not an aircraft-specific performance calculation
The tool does not know aircraft weight, configuration, runway state, wind, engine condition, or POH/AFM performance procedures. Those inputs must be handled by the applicable aircraft-specific method.
Sources and Verification
The calculator and guide use FAA definitions for pressure altitude and aviation pressure terminology, plus National Weather Service equations for the Advanced standard-atmosphere path. The worked example was independently recomputed from the displayed formula and cross-checked against the calculator logic.
- FAA Pilot’s Handbook of Aeronautical Knowledge, FAA-H-8083-25C — Supports the definition of pressure altitude, the 29.92 inHg standard datum reference, related altitude terminology, and the distinction between pressure altitude and density altitude.
- FAA Aeronautical Information Manual, Section 7-2 — Barometric Altimeter Errors and Setting Procedures — Supports the 29.92 inHg standard setting and the approximate 1,000 ft altitude change associated with a 1 inHg altimeter-setting difference.
- FAA Order JO 7900.5E, Surface Weather Observing — Defines altimeter setting, field elevation, pressure altitude, standard atmosphere, station pressure, and density altitude as distinct aviation weather quantities.
- FAA Aeronautical Information Manual, Section 7-1 — METAR Key — Documents the U.S. A-prefix altimeter group and Q-prefix hectopascal convention used in METAR coding examples.
- National Weather Service Station Pressure Formula — Provides the station-pressure relationship used by the calculator’s Advanced method to convert field elevation and altimeter setting into station pressure.
- National Weather Service Pressure Altitude Formula — Provides the standard-atmosphere pressure-altitude equation from station pressure.
Pressure Altitude FAQ
These questions address common pressure-altitude interpretation and input issues that are not obvious from the numerical result alone.
Does temperature affect pressure altitude?
Temperature is not required for the basic field-elevation plus altimeter-setting pressure-altitude calculation. Temperature is used when correcting pressure altitude for nonstandard air density, which leads to density altitude and affects aircraft performance.
Can pressure altitude be negative?
Yes. Pressure altitude is referenced to the standard-atmosphere pressure surface, not the ground. Under sufficiently high pressure or at a below-sea-level location, the corresponding pressure altitude can be below zero.
Is pressure altitude MSL or AGL?
Pressure altitude is neither a simple AGL height nor the same thing as true MSL altitude. It is the altitude in the standard atmosphere corresponding to pressure, referenced to the 29.92 inHg standard datum. True altitude is measured above mean sea level, while absolute altitude is height above terrain.
What do A2992 and Q1013 mean in a METAR?
A2992 represents an altimeter setting of 29.92 inHg. Q1013 represents QNH of 1013 hPa. The calculator supports both pressure-unit conventions, so select the matching unit before entering the value.
Why does the NWS pressure altitude calculator ask for station pressure?
The NWS direct pressure-altitude equation uses uncorrected station pressure as its input. The calculator above is designed around the more common pilot workflow of field elevation plus altimeter setting/QNH; its Advanced method derives station pressure internally before applying the NWS pressure-altitude equation.