Definition
A temperature scale on which, at standard sea level pressure, water freezes at 32 degrees and boils at 212 degrees. Commonly used in the United States and abbreviated °F.
Plain English
A way of measuring temperature where freezing water is 32 and boiling water is 212. It is the temperature scale most Americans grew up with.
Context Anchor
Seen in aircraft performance discussions and charts when temperature is shown in degrees Fahrenheit, such as the standard sea-level temperature of 59 °F.
Derivation
Named after Daniel Gabriel Fahrenheit, an 18th-century German physicist who developed the scale and the mercury thermometer. Knowing the name comes from a person, not a technical word, helps avoid trying to read meaning into the word itself.
Why Pilots Care
US performance charts and density altitude tables are often calibrated in Fahrenheit, directly affecting takeoff distance, climb rate, and engine performance predictions.
Intuition Check
If you see a temperature like 30 and assume it is warm, check the scale. 30°F is below freezing. 30°C is a warm summer day. Same number, very different flying conditions.
Example Sentence 1
The outside air temperature gauge read 50 degrees Fahrenheit, so the pilot converted it to about 10 degrees Celsius before using the density altitude chart.
Example Sentence 2
Higher Fahrenheit readings reduce air density and lengthen the calculated takeoff roll.