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Pressure and density altitude calculator
Pressure and density altitude, flight levels on QNH, and the transition level.
Pressure and density altitude
Load an airport’s elevation, QNH and temperature, or type your own.
Optional. Don’t know the code? Use the airport search.
Flight level to altitude
Uses the QNH above.
Transition level
The lowest flight level that leaves enough room above the transition altitude, using the QNH above. The highlighted row is today’s.
The terms
- QNH is the pressure setting that makes an altimeter read the airport’s elevation on the ground.
- QFE makes it read zero on the runway instead. It’s the actual pressure at that height.
- Pressure altitude is what the altimeter reads with the standard 1013.25 hPa (29.92 inHg) set. A flight level is pressure altitude in hundreds of feet.
- Density altitude is pressure altitude corrected for temperature. Hot air is thin, so on a hot day at a high airport an aircraft performs as if it were much higher.
The rules of thumb
Near sea level 1 hPa is about 27–30 ft, so a QNH of 1000 hPa puts pressure altitude about 360–400 ft above your altitude. Density altitude rises about 120 ft for each degree above standard. This calculator uses the full standard-atmosphere formulas for dry air, so its answers can differ a little from these shortcuts, and from the Weather page, which uses the shortcuts.
Transition altitude and level
Climbing through the transition altitude, pilots change to 1013 and talk in flight levels. Descending through the transition level, they change to QNH and talk in altitudes. The gap between them is the transition layer, where nobody is cleared to fly level. Because a flight level’s real height moves with the pressure, a low QNH pushes the transition level up to keep that layer thick enough.
Published tables can differ from this calculator, so a real airport’s published transition level always takes priority. Some countries, such as the United States, use a fixed transition altitude and level. The flight levels guide explains more.
Quick answers
How do you calculate pressure altitude?
Set 1013 hPa and read the altimeter. Or take your altitude and add (1013 − QNH) × about 27–30 ft, or in inches, (29.92 − altimeter setting) × 1,000 ft.
How do you calculate density altitude?
As a shortcut, pressure altitude + 120 ft for each degree above the standard temperature. This calculator uses the full formula for dry air, so its answer can differ a little.
What is the difference between QNH and QFE?
With QNH set, the altimeter reads the airport’s elevation on the ground. With QFE set, it reads zero there.
What is the transition level?
The lowest flight level available above the transition altitude. A descending aircraft changes from 1013 to QNH as it passes through it.
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For training and simulation only. These calculators are for learning and for games. Their results are automatic, and they don’t account for everything a real operation does. Never use them for real flight planning, navigation or air traffic control. Use your official charts, approved tools and procedures.
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