How to Convert Between Fahrenheit and Celsius

Learn an easy way to convert temperatures from Fahrenheit to Celsius (and vice versa)—and check if the weather outside is frightful.

Jason Marshall, PhD,
May 3, 2013
Episode #086

How to Convert Between Fahrenheit and Celsius

Oh the weather outside is frightful, but the fire is so delightful. And since we’ve no place to go…let’s talk about temperature conversions!

I know, you actually have lots of places to go and a bunch of important things to do. But with wintry weather starting to sweep across the northern hemisphere, there’s no better time for us to learn how to easily convert between the two most commonly used temperature scales: Fahrenheit and Celsius. That way you’ll be able to do the conversions and tell your friends on the other side of the world who use the other temperature scale all about that frightful weather and delightful fire.!

What are the Fahrenheit and Celsius Scales?

How do we measure temperature? Well, we use a thermometer. And depending on where you live, those thermometers have scales marked in degrees Fahrenheit or degrees Celsius. Actually, a lot of thermometers have both scales marked on them, which means that there must be a way to convert between them. We’ll get to that soon enough, but first let’s look a bit deeper at the two most commonly used temperature scales.

First, Mr. Fahrenheit. This scale dates back to 1724 and rather inconveniently (since it’s hard to remember) says that water freezes at 32 degrees and boils at 212 degrees. In contrast, Mr. Celsius’s temperature scale proposed around 1742 rather conveniently says that water freezes and boils at the easy to remember temperatures of 0 and 100 degrees. The Fahrenheit scale is the primary temperature scale in the United States and a smattering of other places around the world, but the Celsius scale is used in the metric system and is by far the standard of choice everywhere else.

What are Some Common Temperatures?

Besides the temperatures at which water freezes and boils, it’s handy to have a few additional point-of-reference temperatures to give you a feel for the two scales. For example, the temperature of a pleasant day at the beach is 75 degrees Fahrenheit or 24 degrees Celsius; the temperature of the human body is about 98.6 degrees Fahrenheit or 37 degrees Celsius; and a typical oven baking temperature is about 350 degrees Fahrenheit or approximately 175 degrees Celsius.

How to Convert From Fahrenheit to Celsius

But how can you take any temperature given in degrees Fahrenheit and convert it into a temperature in degrees Celsius? The quick and dirty tip is to remember that:

temperature in degrees Celsius = (temperature in degrees Fahrenheit – 32) / 1.8

For example, to convert a temperature of 212 degrees Fahrenheit (which is the boiling point of water) into a temperature on the Celsius scale, simply subtract 32 from 212 to get 212 – 32 = 180, and then divide this number by 1.8 to get 180 / 1.8 = 100 degrees Celsius. That’s it!

How can you remember that you have to subtract 32 and not add 32 and that you have to divide by 1.8 and not multiply by 1.8 in this conversion? The quick and dirty way is to remember that the temperature of something in degrees Celsius is always a smaller number than its temperature in degrees Fahrenheit (at least for positive temperatures). As we just saw, the boiling point of water, 212 degrees Fahrenheit, corresponds to 100 degrees Celsius…which is a smaller number. If you can remember that, it’ll be easy to also remember that when converting from Fahrenheit to Celsius you have to subtract 32 and then divide by 1.8 since both of these things make the temperature smaller…exactly as it must be.

How to Convert from Celsius to Fahrenheit

[[AdMiddle]How about going the other way and converting from a temperature in degrees Celsius to degrees Fahrenheit? Well, if you play around with the equation we just learned, you’ll find that you can convert from degrees Celsius to degrees Fahrenheit by first multiplying by 1.8 and then adding 32 to the result, like this:

temperature in degrees Fahrenheit = (temperature in degrees Celsius • 1.8) + 32

For example, imagine you’re traveling in Europe and are told to stay hydrated since it’s going to be 40 degrees Celsius. How hot is that? Well, just multiply 40 by 1.8 to get 40 • 1.8 = 72 and then add 32 to this to find that 40 degrees Celsius is equal to 72 + 32 = 104 degrees Fahrenheit. So, yes, that’s mighty hot indeed! And that’s all there is to converting from one temperature scale to another.

Number of the Week

Before we finish up for today, it’s time for this week’s featured number, conversion, or tip from my post on QDT’s blog The Quick and Dirty. This week we have two featured numbers: 354 and –380 degrees Fahrenheit. What are they? The first is the average temperature on the surface of the planet Mercury—which is as hot as an oven!—and the second is the average temperature on the surface of the icy body in the outskirts of our solar system formerly known as the planet Pluto (it’s still known as Pluto, it’s just not considered a planet anymore).

What are these temperatures in degrees Celsius? Well, you now have all the tools you need to figure this out. So give it a shot and then head over to my post on The Quick and Dirty blog to check your answers.

Wrap Up

Okay, that’s all the math we have time for today. Remember to become a fan of the Math Dude on Facebook where you’ll find a new featured number or math puzzle posted every weekday. And if you’re on Twitter, please follow me there too. Finally, if you have math questions, feel free to send them my way via Facebook, Twitter, or by email at mathdude@quickanddirtytips.com.

Until next time, this is Jason Marshall with The Math Dude’s Quick and Dirty Tips to Make Math Easier. Thanks for reading, math fans!

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Thermometer image from Shutterstock

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