<blockquote>
<p>During the late 1970s and early 1980s, I was told (by more than one teacher) that the degree symbol should be omitted when using the Celsius scale: 20 C, not 20 °C. In fact, I was taught to say just &quot;Celsius&quot; not &quot;degrees Celsius&quot;.</p>
</blockquote>
<p>You were taught incorrectly. It is degrees Celsius, symbol °C. Quoting from the <a href="https://www.bipm.org/en/search?p_p_id=search_portlet&amp;p_p_lifecycle=2&amp;p_p_state=normal&amp;p_p_mode=view&amp;p_p_resource_id=%2Fdownload%2Fpublication&amp;p_p_cacheability=cacheLevelPage&amp;_search_portlet_dlFileId=41483053&amp;_search_portlet_priv_r_p_javax.portlet.action=search&amp;_search_portlet_priv_r_p_source=BIPM&amp;_search_portlet_priv_r_p_p_p_lifecycle=1&amp;_search_portlet_priv_r_p_formDate=1714993717741&amp;_search_portlet_priv_r_p_query=celsius" rel="nofollow noreferrer">International Bureau of Weights and Measures (BIPM, the acronym is French)</a>,</p>
<blockquote>
<p>The unit of Celsius temperature is the degree Celsius, symbol °C, which is by definition equal in magnitude to the unit kelvin. A difference or interval of temperature may be expressed in kelvins or in degrees Celsius, the numerical value of the temperature difference being the same in either case. However, the numerical value of a Celsius temperature expressed in degrees Celsius is related to the numerical value of the thermodynamic temperature expressed in kelvins by the relation
<span class="math-container">$$t/°C = T/K − 273.15$$</span>
(see 5.4.1 for an explanation of the notation used here).</p>
</blockquote>
<blockquote>
<p>The kelvin and the degree Celsius are also units of the International Temperature Scale of 1990 (ITS-90) adopted by the CIPM in 1989 in Recommendation 5 (CI-1989, PV, 57, 115). Note that the ITS-90 defines two quantities T90 and t90 which are close approximations to the corresponding thermodynamic temperatures T and <span class="math-container">$t$</span>.</p>
</blockquote>
<p>THE BIPM is the international organization that maintains the International System of Units (SI). Their wording by definition is the correct wording.</p>

CC BY-SA 4.0
2024-05-08T15:32:22.773Z
For a standards document, that's remarkably easy to read.  Though it documents SI as it is today, one of the the Appendices has lots of clues about differences from older versions.  For example, it _was_ °K (_degrees_ Kelvin) until 1967.  Celsius (and centigrade) always required the degree symbol according to BIPM.  I still wonder why I was taught to drop it.  I recall having a thermometer from the 1970's that had °F on one side and C (no degrees) on the other.  I've been searching to see if I happen to have a photo of it.
Adrian McCarthy
CC BY-SA 4.0
2024-05-06T11:07:04.660Z
2024-05-06T11:13:08.637Z
2024-05-06T11:13:08.637Z
David Hammen
<p>During the late 1970s and early 1980s, I was told (by more than one teacher) that the degree symbol should be omitted when using the Celsius scale:  <strong>20 C</strong>, not <strong>20 °C</strong>.  In fact, I was taught to say just &quot;Celsius&quot; not &quot;degrees Celsius&quot;.</p>
<p>While I earned an undergraduate degree in physics (1985-1989), I continued to omit the &quot;degrees&quot; as I had been taught.  Nobody ever called me out on it.</p>
<p>But it's clear that the current convention is to include degrees.</p>
<p><strong>Was there ever a style guide that deemed it incorrect to use degrees with Celsius?</strong></p>
<p><strong>If so, when did the convention shift back?</strong></p>
<p>I have some theories, but I've been unable to find evidence to support any explanation.  I'm less interested in more theories than I am of citations style guides or educational materials that can shed light on this.</p>
<hr />
<p>Some context: In that late 1970s, the U.S. made an effort to teach the general population about the metric system with the intent of switching over to it.  That included public service announcements, educational television, and units on the metric system in public school curriculum.  Though a few things did &quot;go metric,&quot; we still primarily use U.S. customary units in most contexts outside engineering, medicine, or science.</p>

CC BY-SA 4.0
2024-05-04T22:32:28.653Z
The unit "C" is for coulomb,.  If you don't include the degree symbol for celsius it is incorrect.  The degree symbol is omitted when using kelvin.  This is because kelvin is an absolute scale that starts at zero, so it doesn't need degrees.
f.thorpe
CC BY-SA 4.0
2024-05-06T11:20:07.367Z
Perhaps you were taught to just say kelvins rather than degrees kelvin. Note the lower case spelling of "kelvin". Getting ones name lower cased in the form of an officially recognized unit is about as high an honor as honors get in physics.
David Hammen
CC BY-SA 4.0
2024-05-06T11:26:25.193Z
Note also that the official spelling of temperature in the Celsius scale is "degrees Celsius", with an upper case "C". The BIPM did not posthumously honor Celsius with a lower case name. But they did recognize the Celsius temperature scale as an approved derived set of units.
David Hammen
CC BY-SA 4.0
2024-05-06T12:34:39.300Z
I received my degree in physics a decade before you. At that time, instructors hammered us on **not** using "degrees Kelvin", to just use "kelvins". Perhaps some of those college instructors who graduated with me later went overboard on also not using "degrees Celsius". The distinction is important. The Kelvin temperature scale is an absolute temperature scale, while the Celsius temperature scale is not. The degree symbol is not needed with the Kelvin scale and also Rankin scale because they are absolute, but is needed with the Celsius and also Fahrenheit scales because they are not absolute.
David Hammen
CC BY-SA 4.0
2024-05-06T15:58:03.713Z
Also note that, like every other units except angles, one needs to add a (non-breaking) space between the value and the °C symbol. I see "20°C" too often, it is incorrect.
Jean-Marie Prival
CC BY-SA 4.0
2024-05-07T13:48:46.653Z
@David Hammen:  I know not to use "degrees" with Kelvin.  One of my theories is that  somebody preparing educational guides back in the 1970s didn't understand the  distinction between Kelvin and the other scales and incorrectly assumed that you don't use "degrees" with "metric" scales.
Adrian McCarthy
CC BY-SA 4.0
2024-05-08T12:16:36.693Z
In addition, the degree symbol was not on a mechanical typewriter, which is what most of us had to use in the late 1970s / early 1980s. LaTeX was there, but one had to have a mainframe computer account to use it. Laptops and personal computers didn't become common until the 1990s. So you were probably given a pass for omitting the degree symbol.
David Hammen
CC BY-SA 4.0
2024-05-08T15:37:30.397Z
@DavidHammen: Mechanical typewriters were missing many common symbols.  Mine didn't even have 0 or 1.  You used capital O and lowercase L instead.  Accent marks, underscores, and most math symbols had to be drawn by hand.
Adrian McCarthy
<temperature>
Celsius or degrees Celsius?
Adrian McCarthy
# Celsius or degrees Celsius?

(Asked by: username_0 on 2024-05-04)

During the late 1970s and early 1980s, I was told (by more than one teacher) that the degree symbol should be omitted when using the Celsius scale: **20 C**, not **20 °C**. In fact, I was taught to say just "Celsius" not "degrees Celsius".

While I earned an undergraduate degree in physics (1985-1989), I continued to omit the "degrees" as I had been taught. Nobody ever called me out on it.

But it's clear that the current convention is to include degrees.

**Was there ever a style guide that deemed it incorrect to use degrees with Celsius?**

**If so, when did the convention shift back?**

I have some theories, but I've been unable to find evidence to support any explanation. I'm less interested in more theories than I am of citations style guides or educational materials that can shed light on this.

---

Some context: In that late 1970s, the U.S. made an effort to teach the general population about the metric system with the intent of switching over to it. That included public service announcements, educational television, and units on the metric system in public school curriculum. Though a few things did "go metric," we still primarily use U.S. customary units in most contexts outside engineering, medicine, or science.

**Tags:** temperature

> **Comments:**
> **username_1**: The unit "C" is for coulomb,.  If you don't include the degree symbol for celsius it is incorrect.  The degree symbol is omitted when using kelvin.  This is because kelvin is an absolute scale that starts at zero, so it doesn't need degrees.  
> **username_2**: Perhaps you were taught to just say kelvins rather than degrees kelvin. Note the lower case spelling of "kelvin". Getting ones name lower cased in the form of an officially recognized unit is about as high an honor as honors get in physics.  
> **username_2**: Note also that the official spelling of temperature in the Celsius scale is "degrees Celsius", with an upper case "C". The BIPM did not posthumously honor Celsius with a lower case name. But they did recognize the Celsius temperature scale as an approved derived set of units.  
> **username_2**: I received my degree in physics a decade before you. At that time, instructors hammered us on **not** using "degrees Kelvin", to just use "kelvins". Perhaps some of those college instructors who graduated with me later went overboard on also not using "degrees Celsius". The distinction is important. The Kelvin temperature scale is an absolute temperature scale, while the Celsius temperature scale is not. The degree symbol is not needed with the Kelvin scale and also Rankin scale because they are absolute, but is needed with the Celsius and also Fahrenheit scales because they are not absolute.  
> **username_3**: Also note that, like every other units except angles, one needs to add a (non-breaking) space between the value and the °C symbol. I see "20°C" too often, it is incorrect.  
> **username_0**: @username_2:  I know not to use "degrees" with Kelvin.  One of my theories is that  somebody preparing educational guides back in the 1970s didn't understand the  distinction between Kelvin and the other scales and incorrectly assumed that you don't use "degrees" with "metric" scales.  
> **username_2**: In addition, the degree symbol was not on a mechanical typewriter, which is what most of us had to use in the late 1970s / early 1980s. LaTeX was there, but one had to have a mainframe computer account to use it. Laptops and personal computers didn't become common until the 1990s. So you were probably given a pass for omitting the degree symbol.  
> **username_0**: @username_2: Mechanical typewriters were missing many common symbols.  Mine didn't even have 0 or 1.  You used capital O and lowercase L instead.  Accent marks, underscores, and most math symbols had to be drawn by hand.  

---

## 1 answers

### Answer by username_2 on 2024-05-06. Score: 4 | Accepted answer

> During the late 1970s and early 1980s, I was told (by more than one teacher) that the degree symbol should be omitted when using the Celsius scale: 20 C, not 20 °C. In fact, I was taught to say just "Celsius" not "degrees Celsius".

You were taught incorrectly. It is degrees Celsius, symbol °C. Quoting from the [International Bureau of Weights and Measures (BIPM, the acronym is French)](https://www.bipm.org/en/search?p_p_id=search_portlet&p_p_lifecycle=2&p_p_state=normal&p_p_mode=view&p_p_resource_id=%2Fdownload%2Fpublication&p_p_cacheability=cacheLevelPage&_search_portlet_dlFileId=41483053&_search_portlet_priv_r_p_javax.portlet.action=search&_search_portlet_priv_r_p_source=BIPM&_search_portlet_priv_r_p_p_p_lifecycle=1&_search_portlet_priv_r_p_formDate=1714993717741&_search_portlet_priv_r_p_query=celsius),

> The unit of Celsius temperature is the degree Celsius, symbol °C, which is by definition equal in magnitude to the unit kelvin. A difference or interval of temperature may be expressed in kelvins or in degrees Celsius, the numerical value of the temperature difference being the same in either case. However, the numerical value of a Celsius temperature expressed in degrees Celsius is related to the numerical value of the thermodynamic temperature expressed in kelvins by the relation
> $$t/°C = T/K − 273.15$$
> (see 5.4.1 for an explanation of the notation used here).

> The kelvin and the degree Celsius are also units of the International Temperature Scale of 1990 (ITS-90) adopted by the CIPM in 1989 in Recommendation 5 (CI-1989, PV, 57, 115). Note that the ITS-90 defines two quantities T90 and t90 which are close approximations to the corresponding thermodynamic temperatures T and $t$.

THE BIPM is the international organization that maintains the International System of Units (SI). Their wording by definition is the correct wording.

> **Comments:**
> **username_0**: For a standards document, that's remarkably easy to read.  Though it documents SI as it is today, one of the the Appendices has lots of clues about differences from older versions.  For example, it _was_ °K (_degrees_ Kelvin) until 1967.  Celsius (and centigrade) always required the degree symbol according to BIPM.  I still wonder why I was taught to drop it.  I recall having a thermometer from the 1970's that had °F on one side and C (no degrees) on the other.  I've been searching to see if I happen to have a photo of it.  

---

