Calculator Inputs
Select a calculation mode, enter the available aviation data, and choose either a quick approximation or an atmospheric-equation method.
Saved Calculation History
History is stored only in this browser with local storage.
Formula Used
The calculator offers two calculation styles. The quick method follows the common cockpit and training approximation. The atmospheric-equation method converts the reported pressure to station pressure and then applies an inverse standard-atmosphere relationship.
Quick pressure-altitude approximation
When the altimeter setting is lower than 29.92 inHg, the correction becomes positive and pressure altitude rises above field elevation. When the setting is higher than 29.92 inHg, the correction becomes negative and pressure altitude falls below field elevation.
ISA pressure relationship
h = (T₀ / L) × [1 − (P / P₀)^(RL / g)]
The precise option uses a tropospheric standard-atmosphere model. It remains an educational implementation and may differ from approved instruments, official tables, local procedures, or atmosphere models used by a specific authority.
Density altitude methods
Detailed density altitude = ISA altitude with matching calculated moist-air density
The detailed method computes water-vapor pressure, dry-air partial pressure, moist-air density, and then finds the standard-atmosphere altitude with equivalent density. Humidity usually changes density altitude less than temperature, but it can still matter in hot and humid conditions.
How to Use This Calculator
1. Choose a mode
Use the normal elevation-and-altimeter mode for most planning examples. Select station pressure when a reliable uncorrected station pressure is available. Inverse modes solve for an altimeter setting or elevation. Batch mode processes several locations together.
2. Select a method
The quick approximation is familiar and easy to audit. The ISA option uses pressure equations and supports a custom standard pressure, local-gravity adjustment, and geopotential conversion.
3. Enter units carefully
Choose feet or meters for altitude. Pressure may be entered as inHg, hPa, millibars, kilopascals, or pascals where supported. A value near 1013 is probably hPa, while a value near 29.92 is probably inHg.
4. Review the result
Compare pressure altitude with field elevation, check the method label, and review the station pressure and ISA temperature. Enable density altitude when outside air temperature and moisture information are available.
Practical workflow
- Verify airport elevation using an official chart or airport publication.
- Obtain a current altimeter setting from an authorized weather or air traffic source.
- Confirm whether the report uses inHg or hPa.
- Calculate pressure altitude and compare it with the aircraft performance chart inputs.
- Add temperature and humidity information when density altitude is required.
- Use the aircraft flight manual or pilot operating handbook for takeoff, climb, and landing performance.
Pressure Correction Chart
The chart shows the approximate pressure-altitude correction at a zero-foot reference elevation. Positive values indicate pressure altitude above elevation. Negative values indicate pressure altitude below elevation.
Understanding Aviation Altitudes
Indicated altitude
Indicated altitude is the value displayed by an altimeter when the selected pressure setting is applied. Instrument error, installation error, pressure variation, and temperature may separate indicated altitude from true altitude.
Pressure altitude
Pressure altitude is the altitude in the standard atmosphere corresponding to a pressure level. It is the value an altimeter would indicate when set to the standard pressure reference, subject to instrument and system behavior.
Density altitude
Density altitude is pressure altitude corrected for nonstandard temperature, with humidity included in more detailed methods. Aircraft performance generally decreases as density altitude increases.
True altitude
True altitude is the actual vertical distance above mean sea level. It may differ from indicated altitude when atmospheric temperature differs from standard conditions.
Absolute altitude
Absolute altitude describes vertical distance above the terrain directly below the aircraft. Radar altimeters and terrain data may be used to estimate this quantity in appropriate operations.
Flight level
A flight level is a pressure surface referenced to standard pressure. Transition-altitude and transition-level procedures vary by country and airspace, so the displayed guide is not operational authority.
Worked Examples
Example 1: Lower-than-standard pressure
An airport elevation is 2,000 feet and the altimeter setting is 29.42 inHg. The pressure difference is 29.92 − 29.42 = 0.50 inHg. Multiplying by 1,000 gives a 500-foot positive correction. The approximate pressure altitude is therefore 2,500 feet.
Example 2: Higher-than-standard pressure
An airport elevation is 4,500 feet and the altimeter setting is 30.22 inHg. The pressure difference is 29.92 − 30.22 = −0.30 inHg. The correction is approximately −300 feet, producing an approximate pressure altitude of 4,200 feet.
Example 3: Hectopascal input
An altimeter setting of 1000 hPa is first converted to approximately 29.53 inHg. At a field elevation of 1,000 feet, the quick correction is close to 390 feet, so pressure altitude is about 1,390 feet. The ISA equation option can produce a slightly different value because it does not assume an exactly linear 1,000-foot change per inHg.
Example 4: Density altitude
Suppose pressure altitude is 5,000 feet, where ISA temperature is roughly 5 °C. If outside air temperature is 30 °C, the temperature is about 25 °C above ISA. The quick density-altitude correction is approximately 120 × 25 = 3,000 feet, giving an estimated density altitude near 8,000 feet. Always use approved performance data for operational decisions.
Validation, Limitations, and Good Data Practices
A useful calculator must do more than produce a number. It should help users detect unit mistakes, unrealistic pressures, stale weather, and confusion between station pressure and sea-level-corrected pressure. This implementation validates common ranges and displays warnings, but it cannot verify the authority, age, location, or quality of entered data.
Altimeter settings are often reported as QNH or an equivalent sea-level pressure setting. Station pressure is the pressure measured at station elevation without reducing it to sea level. Entering QNH in the station-pressure field can produce a substantially incorrect pressure altitude. Similarly, typing 1013 into an inHg field is an obvious unit mismatch, while typing 29.92 into an hPa field is another.
The quick formula uses 29.92 inHg and a fixed 1,000 feet per inHg conversion. That fixed slope is easy to understand but only approximate. The ISA method models a standard lapse rate and uses pressure exponents. Both methods assume an idealized atmosphere and do not reproduce every instrument, atmospheric layer, or approved table.
The atmospheric equation in this file is centered on the tropospheric lapse-rate model. Very high-altitude calculations can require additional standard-atmosphere layers. Latitude-adjusted gravity and geopotential conversion are included as educational refinements, not as substitutes for certified computations.
Reference Values and Unit Conversions
| Reference | Value | Equivalent | Use |
|---|---|---|---|
| Standard sea-level pressure | 29.92 inHg | 1013.25 hPa | Pressure altitude and flight levels |
| Standard sea-level temperature | 15 °C | 59 °F | ISA reference |
| Standard temperature lapse | 1.98 °C per 1,000 ft | 6.5 K per km | Tropospheric approximation |
| Pressure conversion | 1 inHg | 33.8639 hPa | Unit conversion |
| Altitude conversion | 1 m | 3.28084 ft | Unit conversion |
Aviation Glossary
Frequently Asked Questions
Why does lower pressure produce higher pressure altitude?
In the standard atmosphere, pressure decreases as altitude increases. When local pressure is lower than standard for the same elevation, that pressure corresponds to a higher level in the standard atmosphere.
Is pressure altitude the same as density altitude?
No. Pressure altitude is based on pressure relative to a standard atmosphere. Density altitude adjusts pressure altitude for temperature and, in detailed methods, water vapor.
Should I enter QNH or station pressure?
Use QNH or an altimeter setting in the normal elevation-and-altimeter mode. Use actual station pressure only in the station-pressure mode. Do not interchange the two without a valid conversion.
Why do the approximate and ISA methods differ?
The approximate method uses a fixed 1,000-foot correction for each inch of mercury. The atmospheric method uses a nonlinear pressure relationship, so small differences are expected.
Can I paste any METAR?
The browser helper recognizes common pressure and temperature groups, but METAR formatting can vary. Always compare extracted values with the original report before calculating.
Does humidity significantly change density altitude?
Temperature and pressure usually dominate, but humid air is less dense than dry air at the same temperature and pressure. In hot, humid conditions, moisture can further increase density altitude.
Can this calculator replace a pilot operating handbook?
No. Pressure altitude may be one input to an approved performance chart. Aircraft-specific limitations, configuration, weight, runway condition, wind, slope, and procedural factors still apply.
What does the flight-level guide mean?
It simply divides pressure altitude by 100 when the result is at or above the entered transition altitude. Actual transition procedures and valid flight levels depend on the applicable authority and airspace.