Pressure altitude

Pressure altitude is the altitude shown when the altimeter is set to the standard pressure of 29.92 inHg, or 1013.25 hPa. It is a pressure reference, not necessarily the aircraft's height above mean sea level or the ground. Pilots use it for performance calculations, flight levels, and standardizing aircraft data.

How it works

An altimeter senses static pressure and converts it to an altitude using a standard atmosphere model. Changing the altimeter setting changes the displayed altitude without changing the aircraft's physical position. Setting 29.92 inHg makes the displayed value pressure altitude.

At an airport, pressure altitude can also be estimated from field elevation and the local altimeter setting. A setting lower than standard generally produces a pressure altitude higher than field elevation. A setting higher than standard generally produces a pressure altitude lower than field elevation.

Pressure altitude is the starting point for density altitude. Density altitude adds the effect of temperature because warm air is less dense than cold air at the same pressure. The density altitude calculator shows both the pressure and temperature relationship used in its estimate.

Example

Suppose an airport elevation is 2,000 ft and the altimeter setting is 30.12 inHg. Since the setting is higher than 29.92 inHg, the pressure altitude is lower than the field elevation. The exact adjustment depends on the difference between the two settings. A pilot then uses the pressure altitude, temperature, aircraft weight, and POH chart to evaluate performance.

Why it matters

Performance charts commonly use pressure altitude because it lets pilots compare conditions using a common reference. Flight levels also use the standard pressure setting so aircraft operating above the transition altitude share the same pressure reference.

Pressure altitude is not the same as indicated altitude with the local setting. It is also not a substitute for terrain clearance information. Use the correct altimeter setting for local altitude references and follow the applicable operating procedures.

Related terms and tools

• Density altitude
• Indicated airspeed
• Density altitude calculator
• FAA handbooks and manuals