Virtually every country on earth aside from the United States measures temperature in Celsius. This makes sense; Celsius is a reasonable scale that assigns freezing and boiling points of water with round numbers, zero and 100. In Fahrenheit, those are, incomprehensibly, 32 and 212.
This isn’t just an aesthetic issue. America’s stubborn unwillingness to get rid of Fahrenheit temperatures is part of its generally dumb refusal to change over to the metric system, which has real-world consequences. One conversion error between US and metric measurements sent a $125 million NASA probe to its fiery death in Mars’ atmosphere.
Why does the United States have such an antiquated system of measurement? You can blame two of history’s all-time greatest villains: British colonialism and Congress.
Fahrenheit was a great temperature system 300 years ago
Back in the early 18th century, the Fahrenheit measurement system was actually pretty useful. It comes from Daniel Gabriel Fahrenheit, a German scientist born in Poland in 1686.
As a young man, Fahrenheit became obsessed with thermometers. This may seem weird, but measuring temperature was a big problem at the time. No one had really invented a consistent, reliable way to measure temperature objectively. “Fahrenheit was still only twenty-eight years old when he stunned the world by making a pair of thermometers that both gave the same reading,” the University of Houston’s John Lienhard writes. “No one had ever managed to do that before.”
As an early inventor of the thermometer as we know it, Fahrenheit naturally had to put something on them to mark out different temperatures. The scale he used became what we now call Fahrenheit.
Fahrenheit set zero at the lowest temperature he could get a water and salt mixture to reach. He then used a (very slightly incorrect) measurement of the average human body temperature, 96 degrees, as the second fixed point in the system. The resulting schema set the boiling point of water at 212 degrees, and the freezing point at 32 degrees.
In 1724, Fahrenheit was inducted into the British Royal Society, at the time a preeminent Western scientific organization, and his system caught on in the British Empire. “His fellowship in the Royal Society resulted in his thermometer, and thereby his scale, receiving particular acceptance in England,” Ulrich Grigull, the former Chair of Thermodynamics at the Technical University of Munich, writes.
As Britain conquered huge chunks of the globe in the 18th and 19th centuries, it brought the Fahrenheit system (and some other peculiar Imperial measurements, such as feet and ounces) along with it. Fahrenheit became a standard temperature in much of the globe.
Why America still uses it
The Anglophone world ended up being an outlier. By the mid-20th century, most of the world adopted Celsius, the popular means of measuring temperature in the modern metric system. Celsius was invented in 1742 by Swedish astronomer Anders Celsius. “Celsius should be recognized as the first to perform and publish careful experiments aiming at the definition of an international temperature scale on scientific grounds,” Uppsala University’s Olof Beckman writes.
Around 1790, Celsius was integrated into the metric system — itself an outgrowth of the French revolution’s desire to unify the country at the national level. The metric system’s simplicity and scientific utility helped spread it, and celsius, throughout the world.
The Anglophone countries finally caved in the second half of the 20th century. The UK itself began metrication, the process of switching all measurements to the metric system, in 1965. It still hasn’t fully completed metrication, but the modern UK is an overwhelmingly metric country.
Virtually every other former British colony switched over as well. Some did so before even the UK (e.g., India) and others after (e.g., Canada, Australia, South Africa). These changes, all around the same time, prompted the US to consider going metric itself.
It made sense to switch over, both because the metric system is more intuitive and because adopting the same system as other countries would make scientific cooperation much easier. Congress passed a law, the 1975 Metric Conversion Act, that was theoretically supposed to begin the process of metrication. It set up a Metric Board to supervise the transition.
The law crashed and burned. Because it made metrication voluntary, rather than mandatory, the public had a major say in the matter. And lots of people didn’t want to have to learn new systems for temperatures or weights.
“Motorists rebelled at the idea of highway signs in kilometers, weather watchers blanched at the notion of reading a forecast in Celsius, and consumers balked at the prospect of buying poultry by the kilogram,” Jason Zengerle writes in Mother Jones. Organized labor fought it as well, according to Zengerle, so workers wouldn’t have to retrain to learn the new measures.
President Reagan dismantled the Metric Board in 1982, its work in tatters. Congress’s dumb implementation of the law ensured that America would keep measuring temperature in Fahrenheit.
The US is needlessly hurting itself by sticking with Fahrenheit
The bizarre measurements commonly used in the US, including Fahrenheit, are bad for its scientific establishment, its kids, and probably its businesses.
Susannah Locke lays out the case for Celsius and the rest of the metric system very persuasively, but here’s a brief recap. The simpler metric scales make basic calculations easier and thus less error-prone. American companies incur extra costs by producing two sets of products, one for the US and one for the metric using world.
American parents and caregivers are more likely to screw up conversion rates when they give out medicine, sending some children, who are more susceptible to overdoses, to the hospital. Further, American students have to be trained on two sets of measurements, making basic science education even more difficult.
So while Daniel Fahrenheit did the world a solid by inventing a reliable thermometer, his system for measuring temperatures has seen its day. America, it’s time to adopt Celsius — and the rest of the metric system.