Fahrenheit

Fahrenheit (symbol °F) is a temperature scale. It is named after the scientist Daniel Gabriel Fahrenheit, who in the eighteenth century developed a thermometer filled with mercury. The scale uses different values than Celsius, so temperatures that are equivalent in physical reality have different numerical readings in the two systems.

By definition, pure water at standard atmospheric pressure freezes at 32 °F and boils at 212 °F. The difference between these two points is 180 degrees, which means each Fahrenheit degree is smaller than each Celsius degree by a factor of 5/9.

Conversion

To convert Fahrenheit to Celsius: °C = (°F − 32) × 5/9. To convert Celsius to Fahrenheit: °F = °C × 9/5 + 32. The two scales meet at −40, where −40 °C and −40 °F represent the same temperature. Normal human body temperature is commonly given as approximately 98.6 °F, equivalent to 37 °C.

History and definition

Fahrenheit originally set his reference points using phenomena he created by mixing substances—such as ice, water, and salt—and by taking human body temperature. Later, the definition was based on the freezing and boiling points of water. Modern definitions of Fahrenheit derive it from Kelvin and Celsius, without relying on fixed reference substances.

Current use

Most of the world uses Celsius, particularly in science, which works with Kelvin and Celsius. Fahrenheit remains in common daily use in the United States and some associated territories, notably in weather reports and household measurements. Some countries that formerly used it, including the United Kingdom, have switched to Celsius, though Fahrenheit figures still appear occasionally in some media.