Definition
The assumed rate at which temperature decreases with altitude in the International Standard Atmosphere (ISA): approximately 2 degrees Celsius (3.5 degrees Fahrenheit) per 1,000 feet of altitude gain, up to the tropopause.
Plain English
On a standard day, the air gets about 2 degrees Celsius colder for every 1,000 feet you climb. It is the agreed-upon rule of thumb pilots use to predict how cold the air should be at any given altitude.
Context Anchor
Seen in atmospheric pressure, altitude, and aircraft performance discussions when comparing real outside air temperature to the standard reference atmosphere.
Derivation
‘Lapse’ comes from the Latin ‘lapsus,’ meaning ‘a slipping or falling.’ Here it describes how temperature ‘falls off’ as altitude increases. ‘Standard’ refers to the ISA reference values, not to ‘perfect’ or ‘typical’ conditions on any given day.
Why Pilots Care
Accurate application supports reliable density altitude and aircraft performance estimates, especially when actual temperatures deviate from standard.
Grounding Statement
If you climb 1,000 feet in the standard atmosphere, expect the reference temperature to be about 2 °C colder.
Intuition Check
“Standard” does not mean the actual temperature outside will match it. Here, “standard” means a fixed reference used for calculations and performance comparisons.
Example Sentence 1
Sea level was 15 degrees Celsius, so using the standard temperature lapse rate, he expected about 5 degrees Celsius at 5,000 feet.
Example Sentence 2
Performance charts assume the standard temperature lapse rate to provide consistent takeoff and climb data across elevations.