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Atmosphere & Weather
ISA Temperature Calculator by Altitude
Calculate ISA temperature by altitude in feet using the standard-atmosphere lapse rate for pilot training and density-altitude work.
ft
ISA temperature—
Altitude—
ISA lapse from sea level—
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ISA temperature at 5,000 feet
At 5,000 ft, ISA temperature is 15 − (1.98 × 5) = 5.1°C. An OAT of 25°C at that pressure altitude would be ISA +19.9°C.
The lapse-rate expression represents the lower standard atmosphere. It is a reference temperature, not a weather forecast or a lapse rate measured on the day.
Formula and method
In the lower standard atmosphere, ISA temperature decreases from 15°C at sea level at roughly 1.98°C per 1,000 feet.