About this tool
Pressure Altitude Calculator is a free, in-browser tool that converts an airfield's elevation to pressure altitude — the altitude your altimeter would read with the sub-scale set to the standard datum of 29.92 inHg (1013.25 hPa). Enter the field elevation and the current altimeter setting in inches of mercury or hectopascals and the answer appears instantly, computed on your device.
With an inHg setting the tool uses PA = elevation + (29.92 − altimeter) × 1000, since one inch of mercury is worth roughly 1,000 feet. With a hectopascal setting it uses PA = elevation + (1013.25 − QNH) × 27, the standard 27-feet-per-hectopascal approximation. It also echoes the altimeter setting in both pressure units and shows the correction added to or subtracted from field elevation.
Pressure altitude is the starting point for density-altitude, true-airspeed and performance calculations, and it is what you set for flight levels above the transition altitude. This is an estimate for planning and study — not for real-world navigation — so cross-check against official sources and your instruments.
Frequently asked questions
What is pressure altitude?
It is the altitude indicated when the altimeter's sub-scale is set to the standard datum, 29.92 inHg or 1013.25 hPa. It removes local pressure variation so that aircraft at the same flight level share a common reference, and it feeds density-altitude and performance formulas.
How does the calculation differ between inHg and hPa?
For inches of mercury it uses elevation + (29.92 − setting) × 1000. For hectopascals it uses elevation + (1013.25 − QNH) × 27. Both are standard aviation approximations, so the two units give closely matching pressure altitudes.
Why does a low altimeter setting raise the pressure altitude?
Low pressure means the standard datum sits below your actual pressure level, so the aircraft is effectively higher than field elevation in the standard atmosphere. A setting below 29.92 inHg (1013 hPa) therefore pushes pressure altitude above the field elevation.
Is this accurate enough to fly with?
It is a planning and learning estimate, not for real-world navigation. Set your altimeter from an official source and read pressure altitude from the instrument when it matters; verify any figure before operational use.
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