Nearly every country on earth – aside from the United States – measures temperature in Celsius. Celsius is a reasonable scale that assigns freezing and boiling points of water with round numbers, zero and 100. In Fahrenheit, those are 32 and 212.
Only four other nations join the United States and its territories in using Fahrenheit – The Bahamas, Belize, the Cayman Islands and Palau. Canada sometimes uses Fahrenheit, but the official temperature scale is Celsius.
America’s stubborn unwillingness to get rid of Fahrenheit temperatures is part of its refusal to change over to the metric system, which has real-world consequences. One conversion error between U.S. and metric measurements sent a $125 million NASA probe to its fiery death in Mars’ atmosphere.
Why does the United States cling to its antiquated system of measurement? Blame two of history’s all-time greatest villains: British colonialism and the U.S. Congress.
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. Measuring temperature was a big problem at the time. No one had 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.”
Fahrenheit set zero at the lowest temperature he could get a water and salt mixture to reach. He then used a 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, and his system caught on in the British Empire. 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.
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, including India, did so before even the UK and others, including Canada, Australia and South Africa, after. These changes, all around the same time, prompted the U.S. to consider going metric. Congress passed a law, the 1975 Metric Conversion Act, that was supposed to begin the process of metrication. It set up a Metric Board to supervise the transition.
The law failed in its objective 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. Today, only the U.S., Liberia and Burma remain off the metric system, and Burma announced its intent to metricate in 2013.
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.