Why does the United States stick with Fahrenheit instead of Celsius?

If you're American and have ever discussed the weather with someone from another country, you've probably been confused when they mention the temperature being a comfortable 21 degrees. You might think it's a chilly winter day, but to them, it's actually a warm spring afternoon.

This discrepancy arises because almost every other country uses the Celsius scale, part of the metric system, where water freezes at 0 degrees and boils at 100 degrees. Meanwhile, the U.S. and a few other countries—like the Cayman Islands, the Bahamas, Belize, and Palau—stick to Fahrenheit, where water freezes at 32 degrees and boils at 212 degrees. So, the 21 degrees Celsius mentioned earlier is equivalent to a pleasant 70 degrees Fahrenheit in the U.S.

The continued use of Fahrenheit is one of those curious American quirks, much like how the U.S. refers to soccer, while the rest of the world calls it football. So, why does the U.S. stick with a different temperature scale, and why hasn’t it aligned with the rest of the world? There doesn’t seem to be a clear explanation, other than perhaps simple inertia. Americans have a strong aversion to the metric system – a 2015 poll revealed that only 21 percent of people supported switching to metric measures, while 64 percent were opposed.

It might seem logical if Fahrenheit was an outdated system and Celsius was the new, modern alternative, like the New Coke of temperature scales. However, both scales were created just about 20 years apart. Fahrenheit was developed by its namesake, German scientist Daniel Gabriel Fahrenheit, in the early 1700s. He was the first to design alcohol and mercury thermometers that were both accurate and consistent, so that any two of his devices would give the same reading at the same place and time. "His great mechanical skill in working glass enabled him to carry out his designs," as Henry Carrington Bolton described in his 1900 book, "Evolution of the Thermometer, 1592-1743."

Invention of the Fahrenheit Scale

When Fahrenheit first began his work, his primary goal was to create a system that would consistently yield the same temperature reading, not necessarily to compare the temperatures of different objects or times of day. However, when he presented his paper on his temperature system to the Royal Society of London in 1724, he realized that he would also need to establish a standard temperature scale.

Essentially, the Fahrenheit scale was designed with 0 representing the coldest possible temperature for a mixture of ice and salt water, while the highest point was set to body temperature (around 96 degrees Fahrenheit). This gave him a scale that could be divided progressively by 2," explains Don Hillger, a research meteorologist at Colorado State University's Cooperative Institute for Research in the Atmosphere and president of the U.S. Metric Association, a group advocating for a switch to the metric system. "As a result, the freezing point of water was set at 32 degrees F, which isn’t the most practical number. The boiling point of water was set at 212, another number that’s not very useful. The difference between these two temperatures is 180 degrees, again a multiple of 2."

The Celsius Scale

Despite its complexities, the Fahrenheit scale was adopted by the British Empire, which led to its eventual use in the American colonies. Meanwhile, in 1742, Swedish astronomer Anders Celsius introduced a more straightforward system based on multiples of 10. This scale featured a 100-degree difference between the freezing and boiling points of water at sea level. Interestingly, ThoughtCo notes that Celsius initially set water’s freezing point at 100 and boiling at zero, but someone later reversed these values.

The 100-degree symmetry of the Celsius scale made it an ideal match for the metric system, which was formally developed by the French in the late 1700s. However, English-speaking nations stubbornly retained units like the pound and inch, and Fahrenheit continued to be used. In 1961, the U.K. Met Office switched to Celsius for weather forecasts to align with other European countries, and most of the world soon followed suit. The U.S. remains an exception, as the National Weather Service still reports temperatures in Fahrenheit, even though its staff primarily uses Celsius.

"The NWS continues to use Fahrenheit in public reports to cater to the American audience, although many of its operations, such as forecast models, rely on Celsius," explains Hillger. "Moreover, most automated weather stations record temperatures in Celsius. If the U.S. were to switch to metric weather reporting, the Fahrenheit data layer could be eliminated. Still, the NWS is more familiar with the metric system than TV meteorologists, who mainly serve audiences that rarely, if ever, use Celsius—except perhaps near borders with Canada and Mexico?"

Jay Hendricks, head of NIST's Thermodynamic Metrology Group, points out a key advantage of the Fahrenheit scale. "It offers a finer temperature difference within the typical range of ambient temperatures," he explains in an email. "This means that a 1-degree difference between 70°F and 71°F is more noticeable than the difference between 21°C and 22°C. Because the human body can detect such subtle changes in temperature, the Fahrenheit scale provides a greater level of precision for our everyday experience."

However, this advantage disappears when fractional Celsius temperatures are used. "For example, 70 and 71 degrees Fahrenheit convert to 21.1 and 21.7 degrees Celsius," Hendricks notes.