Instrument Flight Rules (IFR) Practice Exam 2025 – The All-in-One Guide to Master Your IFR Certification!

To determine the pressure altitude when given an altimeter setting at a flight level, it's essential to first understand the relationship between pressure altitude and altimeter settings.

Pressure altitude is the altitude indicated on the altimeter when it is set to the standard pressure setting of 29.92 inches of mercury (inHg). The standard atmosphere assumes that 29.92 inHg corresponds to sea level under standard conditions. When flying at a specific flight level, such as FL250, it implies that the aircraft's altitude is 25,000 feet, but this is referenced with the standard altimeter setting.

If the altimeter setting is lower than 29.92 inHg (as it is here with a setting of 28.92), it indicates that the aircraft is actually higher than the indicated altitude, because a lower pressure setting requires reference to a higher actual altitude to maintain level flight.

To calculate the difference, you can convert the altimeter setting into an altitude difference. The standard atmospheric pressure decreases approximately 1 inHg for every 1,000 feet of altitude gain. The difference between the standard setting (29.92) and the actual setting (28.92) is 1.00 inHg. Therefore, you would expect to add