The Celsius temperature scale comes from Anders Celsius, a Swedish astronomer who proposed it in 1742. Celsius was born in Uppsala, Sweden, in 1701 and spent most of his career there as a professor of astronomy. His original scale looked nothing like the one we use today: he set the boiling point of water at 0 degrees and the freezing point at 100 degrees, the reverse of what you see on a modern thermometer.
Anders Celsius and His Original Scale
Celsius came from a scientific family and was appointed Professor of Astronomy at Uppsala University in 1730. He traveled across Europe, published hundreds of observations on the northern lights, and joined a major expedition to Lapland in 1736 to measure the shape of the Earth. Temperature measurement was a side interest, not his primary work.
In 1742, he published a paper in the annals of the Royal Swedish Academy of Sciences describing a thermometer with two fixed reference points: the temperature at which water boils and the temperature at which it freezes. Both are easy to reproduce in a lab, which made the scale practical and consistent. But Celsius assigned 0 to boiling and 100 to freezing, so higher numbers meant colder temperatures. He died just two years later, in 1744, at the age of 42.
Who Flipped the Scale
Shortly after Celsius’s death, the scale was reversed so that 0 represented freezing and 100 represented boiling, the arrangement we use now. Exactly who made this change is disputed. The Swedish botanist Carolus Linnaeus is often credited, but both Linnaeus and Celsius had their thermometers built by the same instrument maker, Daniel Ekström, and it’s unclear whether Linnaeus or Ekström initiated the switch. A French scientist named Jean Pierre Christin has also been suggested as the source of the inversion. Regardless of who flipped it, the reversed version caught on quickly and became the standard.
Why It Was Called “Centigrade” for 200 Years
For most of its history, this scale wasn’t called “Celsius” at all. In southern Europe and English-speaking countries, it was known as the centigrade scale. The word “centigrade” literally means “consisting of a hundred degrees,” referring to the 100 equal divisions between water’s freezing and boiling points. In many other countries, particularly in Scandinavia, people already called it Celsius after its inventor.
The name “centigrade” eventually became a problem. The word described a specific mathematical property of the scale (exactly 100 degrees in the fundamental interval), but as temperature measurement grew more precise, scientists redefined the scale in ways that made that property no longer strictly true. The label had become misleading.
The 1948 Official Rename
In 1948, the Ninth General Conference on Weights and Measures, the international body responsible for measurement standards, officially adopted “degree Celsius” as the name, replacing both “degree Centigrade” and “degree Centesimal.” This wasn’t just a tribute to Anders Celsius. It eliminated the confusion caused by the word “centigrade,” which in some countries (particularly France and Spain) was also used as a unit for measuring angles, where it referred to one hundredth of a right angle.
From that point on, scientific publications, weather forecasts, and international standards gradually shifted to using °C for “degrees Celsius” rather than “degrees centigrade.” You’ll still hear older generations in some English-speaking countries say “centigrade” out of habit, but the official term has been Celsius for over 75 years.
How Celsius Relates to Kelvin
Today’s Celsius scale is formally defined through its relationship to the Kelvin scale, the base unit of temperature in the international system of measurements. One degree Celsius is exactly the same size as one Kelvin. The only difference is the starting point: 0°C equals 273.15 K. So when water freezes at 0°C, that’s 273.15 on the Kelvin scale, and when it boils at 100°C, that’s 373.15 K.
Since 2019, the Kelvin itself has been tied to a fundamental physical constant called the Boltzmann constant, which connects temperature to energy at the molecular level. This means the Celsius scale is no longer defined by the behavior of water in a lab. Water’s freezing and boiling points are still extremely close to 0 and 100, but those values are now consequences of the definition rather than the definition itself. The scale that Anders Celsius built around two pots of water is now anchored to the physics of the universe.
Where Celsius Is Used Today
Nearly every country in the world uses Celsius for everyday temperature measurement. The shift happened gradually over the 19th and 20th centuries as nations adopted the metric system. Japan, for example, switched to metric measurements in 1926 and began using Celsius as its standard. By the mid-20th century, Celsius was the default in science, medicine, and daily life across Europe, Asia, Africa, and South America.
The major holdout is the United States, which still uses Fahrenheit for weather, cooking, and most consumer applications. A handful of other countries and territories also retain Fahrenheit in everyday use, though even American scientists and medical researchers typically work in Celsius. The scale that a Swedish astronomer sketched out in 1742, then someone else quietly flipped upside down, became the way most of the world talks about temperature.