Pressure Altitude Calculator
Calculate pressure altitude from field elevation and altimeter setting. Pressure altitude is the altitude in the standard atmosphere corresponding to the current atmospheric pressure and is used for performance chart calculations, density altitude computation, and flight level operations.
Why This Matters to Pilots
Pressure altitude is the foundation for all performance calculations. Your POH performance charts require pressure altitude (not indicated altitude) as an input for takeoff distance, climb rate, and cruise performance.
Above 18,000 ft MSL (FL180), all altimeters are set to 29.92 inHg, so the altimeter reads pressure altitude directly. Below FL180, understanding the relationship between altimeter setting and pressure altitude helps verify your calculations.
Related Calculators
Frequently Asked Questions
This calculator is for educational and planning purposes only. Always refer to your aircraft's POH/AFM, current NOTAMs, and official weather briefings. No calculator is a substitute for pilot-in-command judgment or CFI guidance. Read our full Safety Disclaimer.
Last reviewed: July 2026
Pressure Altitude in Depth
Pressure altitude is your height above the standard datum plane — the level where the barometric pressure would be exactly 29.92 inches of mercury. It is the reference every performance chart, flight level, and standard-atmosphere table is built upon, which makes it one of the quiet workhorses of aviation. Whenever you set your altimeter to 29.92 above 18,000 feet to fly a flight level, you are reading pressure altitude directly.
For a student pilot, the value of pressure altitude is mostly as the first step toward density altitude and as the entry argument for performance tables. Understanding it clears up a common point of confusion: why the altimeter reads differently when you change the Kollsman window setting, and why two airports at the same field elevation can have different pressure altitudes on the same day.
Step-by-Step: How the Calculation Works
The calculation is straightforward: pressure altitude equals field elevation plus the difference between standard pressure and the current altimeter setting, scaled by roughly 1,000 feet per inch of mercury. In formula form, PA = field elevation + (29.92 − altimeter setting) × 1,000. A setting below 29.92 yields a pressure altitude above field elevation; a setting above 29.92 yields one below it.
This linear approximation of about 1,000 feet per inch is accurate near sea level and remains a practical planning tool throughout the altitudes typical of general aviation. It reflects the fact that the altimeter is fundamentally a barometer calibrated in feet, and adjusting the setting simply shifts the reference from local sea-level pressure to the standard datum.
More Worked Examples
Example 1 — Low pressure system
Field elevation 1,200 ft, altimeter 29.42 inHg. PA = 1,200 + (29.92 − 29.42) × 1,000 = 1,200 + 500 = 1,700 ft. The low pressure raises your pressure altitude 500 feet above the field elevation.
Example 2 — High pressure system
Field elevation 1,200 ft, altimeter 30.42 inHg. PA = 1,200 + (29.92 − 30.42) × 1,000 = 1,200 − 500 = 700 ft. The high pressure lowers your pressure altitude 500 feet below the field elevation, improving performance slightly.
Pilot Decision-Making Context
Pressure altitude by itself rarely drives a go/no-go decision, but it is the gateway to the numbers that do. You use it to enter takeoff, climb, cruise, and service-ceiling charts, and you feed it into the density altitude calculation that ultimately determines your real-world performance. Getting pressure altitude right ensures every downstream figure is trustworthy.
It also matters for altitude awareness in the flight levels and for understanding altimeter errors. On a low-pressure day, forgetting to update your altimeter setting as you fly into an area of lower pressure will leave you lower than the altimeter indicates — the origin of the memory aid "high to low, look out below."
More Questions Answered
When do I actually fly by pressure altitude?
At and above 18,000 feet MSL in the United States, all aircraft set 29.92 inHg and fly flight levels, which are pressure altitudes. Below that, you fly by the local altimeter setting, but pressure altitude still underlies your performance charts.
Is pressure altitude affected by temperature?
No. Pressure altitude depends only on barometric pressure and field elevation. Temperature enters the picture at the next step, when pressure altitude is converted to density altitude.
What is the standard datum plane?
It is the theoretical level in the standard atmosphere where pressure equals 29.92 inHg (1013.25 hPa). Pressure altitude measures height above this plane, giving every aircraft a common reference regardless of local weather.
When do I actually set 29.92 in the altimeter?
In the United States you set the altimeter to 29.92 inHg when climbing through 18,000 feet to fly the flight levels, where all aircraft use pressure altitude so vertical separation stays consistent regardless of local pressure. Below that, you use the local altimeter setting to read true field-referenced altitude.
How large is the pressure-altitude correction on a typical day?
The rule of thumb is about 1,000 feet of pressure-altitude change for every 1.00 inHg the altimeter setting differs from 29.92. A common setting like 29.72 inHg raises pressure altitude roughly 200 feet above field elevation, which is enough to matter for takeoff performance on a marginal runway.
Related Reading & Tools
Want AI explanations, checkride questions, and saved calculations?
FlightCalculators.com is powered by the same team behind SkeyeMentor — the AI-powered FAA ground school. Try SkeyeMentor free.
Try SkeyeMentor Free