How to Write Temperatures in a Document
  • 6-minute read
  • 3rd September 2019

How to Write Temperatures in a Document

Temperatures can present problems when writing an essay or research paper. Do you write them out as words or present them as numerals? And how do you format them? Truth be told, it all boils down to preference, clarity, and whether you’re using a specific style guide. But we do have a few general rules to help you when writing temperatures.

1. Measurement Systems: Celsius, Fahrenheit and Kelvins

One thing you need to know when writing temperatures is which scale to use. The three most common options are Celsius, Fahrenheit, and kelvins:

  • The Fahrenheit scale measures temperatures in degrees Fahrenheit (°F). In this system, water freezes at 32°F and boils at 212°F. This scale used to be common around the world, but now it is mostly used in the US.
  • Most countries outside the US now use the Celsius scale, which measures temperatures in degrees Celsius (°C). On this scale, water freezes at 0°C and boils at 100°C. This system is also known by the older term “centigrade,” but “Celsius” is now standard.
  • The Kelvin scale is used in scientific writing. It differs from the systems above in that it begins at absolute zero (so it has no negative numbers). In addition, this system uses “kelvins” or “K,” not “degrees kelvin.”

We’ll look more at how these systems differ in writing below.

2. Writing Out Numbers: Words or Numerals?

When writing numbers, it’s usually best to write out one through nine (e.g., one, two, three) and use numerals for 10 and higher (e.g., 12, 19, 521). This can vary depending on your style guide, though (e.g., CMoS suggests writing out numbers up to 100), so make sure to check.

So, how does this affect temperatures? As with any numbers, it depends on the context in which you use them. Generally, though, we suggest:

  • Using numerals in scientific or technical writing, particularly if you’re also using the degree symbol or an abbreviated unit of measurement.
  • Spelling out temperatures as words in literary or descriptive writing, especially for smaller or round numbers.

For instance, if you mentioned a low or round temperature in the dialogue of a novel, you’d usually write out the number and unit of temperature:

“I think he’s lost his marbles,” Darcy said with exasperation. “He keeps his house at only three degrees Celsius in the winter!”

And if you were dealing with larger or more complex numbers, you could combine a numeral (for the number) and words (for the unit of measurement) in a single sentence. For instance:

“I wouldn’t touch that,” she said. “It heats up to around 650 degrees Celsius.”

However, in scientific or technical writing, you’d normally use a numeral plus an abbreviated measurement (e.g., “°C” instead of “degrees Celsius”):

In this experiment, the water reached 180°C.

The temperature hit a low of 6°F.

As shown, this applies even for temperatures below ten degrees.

In less formal writing, meanwhile, the choice of whether to use numerals or words is broadly a matter of preference. Numerals are clearer in most cases, though, so keep your reader in mind.

3. To Space or Not to Space?

In the examples above, we’ve written temperatures without a space between the numeral and the unit of measurement when using the degree symbol.

However, some prefer to write temperatures with a space. For instance, the Chicago Manual of Style and the APA Style Guide differ on this point:

Chicago Style: The temperature will reach 120°C.

APA Style: The temperature will reach 120 °C.

If you’re not using a specific style guide, either approach is acceptable. Just make sure to apply consistent spacing across all temperatures in a document.

4. The Kelvin Scale: Temperatures Without Degrees

The Kelvin scale is not measured in “degrees.” Thus, with this temperature scale, you will not need the degree symbol or the word “degrees”:

In this experiment, the water reached 453 K.

In this experiment, the water reached 453°K.

The ideal temperature is 295.15 kelvins.

The ideal temperature is 295.15 degrees kelvin.

Kelvins are often used alongside degrees Celsius in scientific writing, so make sure you don’t confuse how temperatures are written in each system.

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4. Capitalizing Temperature Units

When writing an abbreviated unit of measurement, whether for Celsius, Fahrenheit or kelvins, you will always need a capital letter:

Water boils at 100°C.

Water boils at 100°c.

The triple point of water is 273.16 K.

The triple point of water is 273.16 k.

However, when writing units of measurement as words, the rules vary:

  • Always capitalize Celsius and Fahrenheit, both when referring to the scale (e.g., the Celsius scale) and the unit of measurement (e.g., degrees Celsius).
  • Only capitalize “Kelvin” when referring to the scale (i.e., the Kelvin scale). Do not capitalize “kelvin” when referring to a measurement (e.g., 276.3 kelvins).
  • Never capitalize “centigrade” except at the beginning of a sentence.

5. Temperatures at the Start of a Sentence

It’s best not to start a sentence with a number. If you find yourself doing this, then, you would usually want to rephrase the sentence.

If you really need to use a temperature at the start of a sentence, though, make sure to write the number out as words:

Original: 6°C is the desired temperature.

Correction 1: The desired temperature is 6°C.

Correction 2: Six degrees Celsius is the desired temperature.

Of the “corrected” sentences here, we would suggest the first in scientific or technical writing, since it sticks to the numeral + unit format.

5. Negative Temperatures

In Celsius and Fahrenheit, you can indicate negative temperatures with the words “negative” or “minus” (for temperatures written as words) or a minus sign (for numerals). For example:

Temperatures were as low as negative thirty-four degrees Celsius.

Temperatures were as low as –34°C.

This is not an issue with the Kelvin scale, which does not go below zero.

6. Adding the Degree Symbol in a Microsoft Word Document

In Microsoft Word, you can insert the degree symbol a few different ways. One option is to use the Symbol drop-down menu. Here are the steps:

  • Select the Insert menu on the ribbon
  • Click on the Symbol option
  • From there, choose More Symbols
  • Then, scroll through the options and select the ° symbol

Alternatively, you can use a keyboard shortcut.

If you’re using a PC with a numerical pad, there’s an alt code (shortcut) for the degree symbol: Alt + 0176. Simply hold “alt” and type each number.

If you’re using a Mac, use the Option key instead and type Option + Shift + 8.

7. Consult Your Style Guide

Most style guides include information on temperatures and units of measurement. And if you’re writing for a specific organization, such as a university or your employer, you’ll need to check their style guide for advice.

For instance, the AP Stylebook requires you to use numerals plus the word “degrees.”  As such, if you’d been asked to follow AP rules for an article, you would not use the degree symbol in the document.

But however you choose to format temperatures in your writing, make sure to apply a consistent style in each document. And, when in doubt, you can always have an editing expert check your work for errors or inconsistencies.

Comments (20)
Michael Scibetta
31st December 2020 at 19:45
What about Zero Degree? Should it be written as 0° or +0° or -0°?
    Proofed
    2nd January 2021 at 11:26
    Hi, Michael. Unless there is reason for ambiguity, or you're using a style guide that says to include "+" or "-" for some reason, "0°" plus a unit of measurement for the scale used should be fine.
Gretchen
4th January 2021 at 15:54
What id the proper way to write a freezing temperature range? -65C° to -70C° or -70C° to -65C°
    Proofed
    5th January 2021 at 10:28
    Hi, Gretchen. The order of figures in a range may depend on what you're trying to describe (e.g., whether the temperature is increasing or decreasing). But one thing to note is that the degree symbol should go before the unit for the scale (e.g., "-65°C to -70°C").
Nicole
14th May 2021 at 23:42
What about 4 digit numbers? Use a comma or not? Ex. 1400ºF or 1,400ºF
    Proofed
    19th May 2021 at 09:13
    Hi, Nicole. This is a matter of preference, so either form is fine (unless you're using a specific style guide, in which case it should explain how to format larger numbers).
Kaiya
25th May 2021 at 16:55
What about temperature changes or differences? I have seen recommendations to write out the word degrees (vs abbreviating for actual temperatures) or to put the degree sign after the C.
    Proofed
    25th May 2021 at 17:44
    Hi, Kaiya. Can you clarify the question, perhaps with an example? The rules for writing temperatures don't typically change when you're discussing temperature changes or differences. In terms of using words, figures, symbols, etc., then, the advice in this post should still apply, though make sure to check your style guide if you're using one.
YW Ho
11th August 2021 at 03:46
Kindly to ask, 1. If the required temperature set for freezer is -35°C or lower, which temperature correctly indicated with symbol? ≥-35°C or ≤-35°C? 2. How to read temperature of -35°C or lower? 'maximum temperature at -35°C' or 'minimum temperature at-35°C'? Thanks for answering my questions.
    Proofed
    11th August 2021 at 08:58
    1. The correct sign for "less than or equal to" is "≤" (the other is "more than or equal to"). 2. If -35°C is the highest permitted temperature, you'd want to say "a maximum temperature of -35°C" (or similar, depending on the context).
John McMurtry
6th November 2021 at 23:52
Temperature change should actually be written: C° or F° not with the degree sign first... You would read it as: "The temperature changed 6 Celsius degrees".
    Proofed
    9th November 2021 at 12:18
    Hi, John. That isn't the case in at least most modern style guides (e.g. APA, Chicago). If you can find an example of a style guide that does recommend placing the unit first, though, we can add something to the post that mentions it.
Graziano
1st February 2022 at 08:30
Writing 10°C is wrong. The rule is to separate unit from value by a blank space: 10 °C.
    Proofed
    1st February 2022 at 09:56
    Hi, Graziano. Different style guides have different rules about this. We discuss this in the post in the section "To Space or Not to Space?," so you might want to re-read that part! If you want advice on how a particular style guide recommends writing temperatures, let us know and I'm sure we can help.
Terry K
4th February 2022 at 17:29
In a novel, I'm referencing the body temperature of a sick child several times. For example, "His temperature was holding at 101." Should any body temperatures be written out as 101 degrees or should I be using the degree symbol and F? Thanks!
    Proofed
    7th February 2022 at 10:25
    Hi, Terry. Since this is for a novel, it's really up to you. The only factor you might want to consider is clarity. Will your readers all know that "101" refers to degrees Fahrenheit? If not, then you might want to include that detail on at least the first occasion. You might also want to write out "degrees Fahrenheit" rather than using the degree symbol, especially if the term appears in dialogue, as this it is fairly standard to write out units of measurement in literary prose. But that's largely a matter of stylistic preference.
Katie
28th March 2022 at 20:37
In a technical (but not scientific) document, should '°C' be included in the list of acronyms and abbreviations? Additionally, should it be spelled out at first use within the document, or is '°C' well known enough that it can be abbreviated at first use?
    Proofed
    29th March 2022 at 09:38
    Hi, Katie. The aim of defining abbreviations, both in lists and in the text, is to ensure their meaning will be clear for the audience. As a rule, then, most academic and technical style guides don't require common units of measurement to be introduced or spelled out when used with a numerical value as there's an assumption that readers will know them already (e.g., in APA style, you would write "The water was kept at 22°C," without any need to give the definition of "°C" in the text or in a list of abbreviations). Assuming this is how you're using the unit in your writing, then, you should be fine to use the abbreviated unit by itself throughout. However, some style guides will have exceptions for when a unit of measurement is used without a numeral (e.g., in Chicago and APA style, you would write "several degrees Celsius" rather than "several °C"). And some might recommend defining units of measurement if you think your audience might be unfamiliar with them (e.g., if the unit isn't commonly used in your field of study or if writing for a non-technical audience). As a result, it may be worth checking your style guide for advice if you have one.
Constantine Lapiotis
26th October 2022 at 17:08
What do you mean "Most countries outside the US use Celsius"? ALL COUNTRIES outside the US use Celsius.
    Proofed
    4th November 2022 at 09:58
    Hi, Constantine. There are a few countries besides the US that use Fahrenheit, including Belize and Liberia, so we’ve reflected this in the article. I hope you found it useful.

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