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.
One thing you need to know when writing temperatures is which scale to use. The three most common options are Celsius, Fahrenheit, and kelvins:
We’ll look more at how these systems differ in writing below.
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:
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.
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.
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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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:
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.
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.
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:
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.
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.
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