Temperature Degrees: How Do You Write Them Correctly?

Temperature is one of those things that we mention almost daily, whether it’s to complain about the heat, celebrate a cool day or choose what to wear before going out. However, despite how common it is to talk about degrees, writing them correctly is not always so simple. Have you ever hesitated about putting a space before the symbol? Or if you say degree Celsius or degree Celsius? Here we explain everything in a clear, simple way and with some curiosities that you may not have known.

Celsius, Celsius, or simply grade

In technical and scientific contexts, the correct name is “degree Celsius”, in honor of the Swedish astronomer Anders Celsius, and that is why it is written with an initial capital letter in the surname. However, outside of those more specialized contexts, many people still use the traditional form: “degree Celsius” or even just “degree.” Although the three ways are understood, if you want to be precise and keep up with the most accepted terminology, it is advisable to talk about degrees Celsius.

A curious fact: the word “centigrade” comes from the Latin centum (one hundred) and gradus (step or degree), and referred to the 100 steps between the freezing and boiling point of water. However, in 1948 the term “Celsius” was officially adopted to avoid confusion with the use of the term centigrade in other contexts.

The right symbol: °C

When we write the temperature, the internationally accepted symbol is °C.  This symbol is made up of a small circle (called a degree) followed by the letter C with no space between them. The important thing is to leave a space between the numerical number and the symbol. Thus, the correct thing to do would be to write: 23 °C.  That small space between the number and the symbol is more important than it seems, especially in technical texts, as it can affect the clarity of the message.

A very common mistake is to write the symbol without the space (e.g. 23°C), or worse, replace the small circle with a letter “o” or a zero (23°C or 23°C). These forms are not correct, although in some digital contexts or with typographical limitations they may appear. If it is necessary to use an “o” for technical reasons, it is preferable not to underline it or accompany it with a period, and in any case, it is recommended to simply write “23 degrees”.

Beware of line breaks

Another curious but important detail: the number and symbol should not appear on separate lines. This means that if you’re writing a long text and you just fall between the number and the °C, it’s best to use a non-separation space or any resource that keeps the two elements together. In digital formats this can be easily done with key combinations or layout tools.

And what about other units?

Although Celsius is used in most countries, we sometimes find other units of temperature, such as kelvin or Fahrenheit.

• Kelvin: In scientific contexts, the kelvin is used, which is always written with a lower case letter and without the word “degree” in front of it. Its symbol is simply K (not °K). Thus, the correct thing to do would be to write: 273 K. The kelvin is the unit of the International System for measuring thermodynamic temperature. Interestingly, 0 K is absolute zero, a theoretical temperature at which all molecular motion ceases.
• Fahrenheit: In some countries, such as the United States, the Fahrenheit degree is used, whose symbol is °F. This is how it is written: 98 °F.  This scale was developed by Daniel Gabriel Fahrenheit in 1724 and was originally based on three reference points: the lowest temperature he could obtain with a mixture of ice, water, and salt; the temperature of the human body; and the freezing point of water. In Spanish-speaking countries, it is advisable to convert these values to degrees Celsius to avoid confusion.

An internationally regulated system

All of these temperature units are part of the International System of Units (SI), which is used in most countries around the world and is also part of many national legislations. In addition, there is a complement called the International System of Magnitudes (ISO 80000), which specifies in detail how these values should be represented in the different fields of knowledge.

The SI not only regulates how units are written, but also which symbols should be used, how they should be combined with numbers, and how they should be treated in scientific and academic publications. This ensures international coherence and avoids misunderstandings between scientists from different countries.

Curiosities to remember better

Did you know that the Celsius system originally started the other way around? When Anders Celsius proposed his scale in 1742, the boiling point of water was 0 degrees and the freezing point was 100 degrees. It was his colleague Carl Linnaeus who reversed the scale after Celsius’ death, leaving it as we know it today.

Another curiosity is that the degree symbol (°) is also used for angles, such as in geometry or navigation. Therefore, in technical contexts it is important not to confuse them, and to reserve the symbol ° only for temperature when accompanied by the corresponding letter (C, F).

And here’s a funny anecdote: in 2010, a group of scientists in Germany proposed creating a new unit of measurement for the “subjective cold” one feels when going out in winter undressed. Although it was never formalized, the experiment sparked public interest in thermal perception and its relationship to humidity and wind, which leads us to another very interesting concept: “wind chill.”

Wind chill is not an official unit, but it is often used in meteorology to describe how we actually perceive temperature by taking into account wind or humidity. For example, even if the thermometer reads 5 °C, if there is a strong wind we could feel that it is 0 °C or less. This subjective perception can have a big impact on how we dress, if we go out to play sports or if we decide to stay at home with a blanket and hot chocolate.

In short…

If you want to write the temperature correctly:

• Use “degree Celsius” capitalized in “Celsius” if you’re in a technical context.
• The correct symbol is °C, with a space between the number and the symbol: 25 °C.
• Don’t use zeros, “or” letters, or weird underlines.
• Make sure that the number and symbol are together, without line breaks.
• Kelvin is written without “degree” and with the single letter K.
• Fahrenheit is rarely used outside the U.S. and must be converted to Celsius.
• Don’t confuse the temperature degree symbol with the angle symbol.

Small details that make a difference when you write accurately, especially if you study, work or simply like to express yourself well.

So now you know! The next time you say “It’s so hot!”, make sure you write it correctly as well. 😉