First proposed in 1724 by physicist Daniel Gabriel Fahrenheit (who had also invented the mercury thermometer in 1714), the Fahrenheit temperature scale was once the preferred temperature scale for much of the world, having been spread by the then-global British Empire. Today, however, Fahrenheit has been replaced by the Celsius (and in scientific applications, Kelvin) scale in all but a handful of the world's countries. Chief among these is the United States, which has also resisted the global switch to the metric system of measurement. Most US territories also use Fahrenheit, and some countries officially use both systems.
In addition to the countries listed above, many countries that are officially Celsius countries still use Fahrenheit in some unofficial or informal capacity. In Canada, for example, the weather report is given in Celsius, but recipes typically list oven temperatures in Fahrenheit. Additionally, a journalist writing a newspaper headline about a heat wave in the United Kingdom may choose to use Fahrenheit for dramatic effect, with the thought that 105°F sounds more impactful than 40.55°C.
As a rule, Celsius is regarded as a more user-friendly scale than Fahrenheit. This belief stems largely from the temperatures each scale assigns two well-known temperature waypoints: the freezing point and boiling point of water. In the Fahrenheit system, water freezes at a seemingly arbitrary 32°F and boils at 212°F, which is 180 degrees warmer. On the Celsius scale, by comparison, water freezes at 0°c and boils at 100°C, a mathematically tidier 100 degrees later.
Many countries transitioned from Farenheit to Celsius as part of a larger switch to the metric system, which uses Celsius as its unit of measurement, but expresses them in terms of kelvin. The Kelvin scale, which replaces the word "degrees" with the non-capitalized "kelvin", is based upon the Celsius scale, but places its zero point at absolute zero, the temperature at which a thermodynamic system has the least amount of energy, instead of the freezing point of water. On the kelvin scale, 0 K is equal to −273.15 °C and the boiling point of water is 373 K.
|Waypoint||Fahrenheit (°F)||Celsius (°C)||Kelvin (K)|
|Absolute zero (exactly)||-459.67||-273.15||0|
|Melting point of water (approximate)||32||0||273.15|
|Normal human body temperature (average)||98.6||37||310.15|
|Boiling point of water (approximate)||212||100||373.15|
With so much of the world using Celsius, it is fair to ask why the US, known as a global leader in many areas, would has not officially switched to Celsius as well. The US actually took the first step toward switching to Celsius when Congress passed the 1975 Metric Conversion Act. However, unlike in other countries, whose governments made the switch mandatory, the US government declared the switch optional.
As a result of this difference, only a few industries incorporated Celsius and Kelvin into their operations. For instance, weather thermometers are often made to show both the Fahrenheit and Celsius temperatures, and scientific studies often use Kelvin. However, the majority of the country's people and industries instead opted not to switch. Industries wanted to avoid the expense of retraining their employees and retooling the relevant equipment to use Celsius instead of Fahrenheit, and the average person was reluctant to learn a whole new system.
This reluctance has added a layer of logistical complexity over many business processes in the US. For example, the US National Weather Service (NWS) uses the Celsius scale internally and when communicating with other scientific agencies, but converts temperatures to Fahrenheit when releasing data to the general public.
Proponents of Fahrenheit occasionally put forth the argument that the Fahrenheit scale is more accurate than Celsius (and, by extension, Kelvin). This belief is based upon the notion that Fahrenheit uses a smaller unit of measurement, with 180 Fahrenheit degrees between the freezing and boiling points of water as opposed to only 100 Celsius degrees between the same two values. This difference does make Fahrenheit roughly 60% more likely to express temperatures in whole numbers (see table below), which arguably makes them easier to parse and discuss. But that should not be taken as evidence that Fahrenheit is in any way more accurate than Celsius. As long as temperatures are written with their full decimal values, both scales are equally accurate.
However, temperatures in both scales are made less precise when rounded to the nearest whole number. In such a circumstance, the Celsius scale's larger units mean that a Celsius temperature rounded to the nearest whole digit is slightly more likely to deviate from the actual temperature than the rounded Fahrenheit temperature would, and to a greater degree.
|Fahrenheit (°F)||Celsius (°C)||Fahrenheit (°F)||Celsius (°C)|
|Number of °F whole-number temps within range:||19|
|Number of °C whole-number temps within range:||11|
There are currently only 11 countries that still use Fahrenheit, but there are also 8 countries that use both forms of measurement.