How to Calculate Pressure & Density Altitude (+ Free Calculator)

Understanding how to calculate pressure and density altitude is essential for safe and accurate flight performance. Whether you're preparing for a checkride or planning a hot-day takeoff, the formulas below will help you estimate conditions quickly and accurately. Our new tool here can help you calculate these in seconds, try it out!

The tool uses the formulas commonly relied on to approximate Pressure Altitude, the International Standard Atmosphere temperature at that pressure altitude, and then the Density Altitude. Here are the formulas for each:

Pressure Altitude Formula

To calculate approximate pressure altitude:

Pressure Altitude = Indicated Altitude + (29.92 − Altimeter Setting) × 1000

This gives you your altitude corrected to standard pressure conditions (29.92 inHg).

Example:

Indicated Altitude = 3,500'

Reported Altimeter = 29.65 inHg

Pressure Altitude = 3500 + (29.92 − 29.65) × 1000

Pressure Altitude = 3,770'

ISA Temperature Formula

To calculate the International Standard Atmosphere (ISA) temperature at your altitude:

ISA Temperature = 15 − (Pressure Altitude ÷ 1000 × 2)

This assumes the standard lapse rate of 2°C per 1,000 feet.

Example:

Pressure Altitude = 3,770'

ISA Temp = 15 - (3770 ÷ 1000 × 2)

ISA Temp = 7.46°C

Density Altitude Formula

To calculate density altitude using a rule of thumb:

Density Altitude = Pressure Altitude + 120 × (Outside Air Temp − ISA Temp)

This gives you the "performance altitude" your airplane feels like it’s at, accounting for nonstandard temperatures.

Example:

Pressure Altitude = 3,770'

Outside Air Temp (OAT) = 25°C

ISA Temp = 7.46°C

Density Altitude = 3770 + 120 × (25 − 7.46)

Density Altitude = 5,875'

At higher altitudes above sea level an aircraft will have poorer performance

Final Thoughts

Understanding how to calculate pressure and density altitude is essential for safe flight operations, especially when dealing with high-elevation airports, hot weather, or performance-limited aircraft. This tool gives you a quick and reliable way to estimate both values without needing a chart or app.

If you want to take a deeper dive into the theory and real-world impact of pressure vs. density altitude, check out our full explainer: Pressure Altitude vs. Density Altitude – What Pilots Need to Know

For official references and further reading:

• FAA Pilot’s Handbook of Aeronautical Knowledge – Chapter 7

• FAA Performance Charts Guide (AC 61-23C)

• National Weather Service: Aviation Weather Center

If you found this tool helpful, share it with fellow pilots, student aviators, or instructors, and bookmark it for your next preflight briefing.