Use this calculator for flight-planning study or a first-pass cross-check when all inputs describe the same aircraft, atmospheric condition, and phase of flight.

Pressure altitude (ft)

Pressure altitude of the observation in the standard atmosphere.

OAT (°C)

Observed outside air temperature.

Compute how much the outside air temperature deviates from ISA at the altitude. The tool evaluates the supplied inputs together and returns the named outputs below; it does not infer omitted operating conditions or change the units shown.^[1]

ISA deviation (°C)

OAT minus ISA standard temperature; positive means warmer than standard.

• Do not use a generic calculator in place of the current aircraft flight manual, approved performance data, operating limitations, NOTAMs, weather, or regulations. Real performance changes with configuration, runway condition, altitude, temperature, wind, loading, and technique.
• Use finite inputs in the displayed units and preserve more precision than the final presentation requires. Independently verify safety-critical, financial, compliance, or production decisions.

Cross-check the result against the aircraft flight manual or approved planning system, then apply the required safety margins. Keep signed wind, heading, altitude, speed, and fuel conventions explicit.

• ISA Deviation Calculator

  Compare the outside air temperature with the ISA standard temperature at a pressure altitude.

• Density Altitude ISA Correction Calculator

  Estimate density altitude from pressure altitude and outside air temperature using the ISA lapse rate.

• Density Altitude Calculator

  Compute density altitude from pressure altitude and outside air temperature.