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How to Convert Celsius to Fahrenheit Quickly

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Measuring temperature on a day-to-day basis is generally pretty simple: you’re either warm or cold, and the specific numbers really don’t matter all that much. In science class, however, temperature becomes all about the numbers.


Suddenly, you’re expected not only to quantify temperature, but to attach one of two units: Fahrenheit or Celsius. To make matters worse, you’ll have to learn how to convert between these two measurements.


If you’re sick of reaching for a calculator every time you have to deal with these units, you’re in the right place. Read on to find out how to quickly convert Celsius to Fahrenheit.


What is Celsius?


Let’s start with the basics: what is celsius? Celsius—sometimes called the centigrade scale—is the most common method of quantifying temperature. It is employed by the International System of Units, or the metric system, which is used in all countries except:


  • United States
  • Bahamas
  • Belize
  • Cayman Islands
  • Liberia


Named after Anders Celsius, this system has been around since the early 1700s. In today’s form, you will see it depicted as a degree symbol followed by a capital ‘c’ ( °C).


What is Fahrenheit?


If you live in one of the five countries listed above, you’re probably already familiar with Fahrenheit. The Fahrenheit system’s zero degrees (written as 0°F) came about from the temperature of brine, a combination made from equal parts ice, water, and salt.


Daniel Gabriel Fahrenheit proposed this scale in 1724, and it was later adopted as the primary measurement in the above five countries, as well as on various islands. Unlike Celsius, Fahrenheit is a component of the Imperial system (think of inches, pounds, and gallons). That said, it is not nearly as prevalent in the science community as its metric system counterpart.


Exact Conversion


Now that you know a little bit about Fahrenheit and Celsius, how do you actually convert between the two scales? While the point of this article is to give you some shortcuts, there is unfortunately nothing as exact as the actual formula. Before we continue, let’s make sure you’re familiar with the math.


Celsius to Fahrenheit: (Temperature in Celsius) x 1.8 + 32 = Temperature in Fahrenheit


As an example, let’s say you’re given the temperature 12°C, which you need to convert into Fahrenheit. Here’s how the math plays out:


(12 x 1.8) + 32

(21.6) + 32

= 53.6°F


And there you have it. Now let’s check the reverse.


Fahrenheit to Celsius: ((Temperature in Fahrenheit) – 32)  / 1.8 = Temperature in Celsius


Let’s says you’re given the temperature 82°F, a warm summer day. What would that look like in Celsius? Let’s take a look:


(82 – 32) / 1.8

(50)  / 1.8

= 27.777778°C


As you can see, it didn’t turn out so nice in this example. Oftentimes, the work to convert between temperatures doesn’t make for clean math, and if you don’t have a calculator, the numbers can be downright nasty.


But don’t panic. Luckily, we’ve identified some simplified methods of converting from Fahrenheit to Celsius, and vice versa.

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Shortcut #1: Memorization of Common Values


When in doubt, it can be incredibly helpful to memorize some of the most recurring temperature values. These numbers pop up more than any others, so if you know the conversion values off the top of your head, you can sidestep the entire formula process.


As an added bonus, even if the numbers in a problem don’t correspond to the chart, memorizing the values listed will still give you an idea of whether or not your conversion is reasonable. This allows you to quickly check the accuracy of your math.


Without further ado, here are some of the most common values for Celsius and Fahrenheit.


Celsius (°C) Fahrenheit (°F)
Point of Equality -40 -40
(Very) Cold Day -18 0
Water’s Freezing Point 0 32
Room Temperature 21 70
Body Temperature 37 98.6
Water’s Boiling Point 100 212


Shortcut #2: Approximation


In some cases, if the problem doesn’t call for specificity, you may actually be better off approximating. This makes the math way more manageable, and in most cases, the answer is extremely close to the exact conversion.


Celsius to Fahrenheit: (Temperature in Celsius) x 2 + 30 = Temperature in Fahrenheit


Using the same example as before, let’s see how this plays out.


(12 x 2) + 30

(24) + 30



Only 0.4 degrees off. Not bad, huh?


Fahrenheit to Celsius: ((Temperature in Fahrenheit) – 30)  / 2 = Temperature in Celsius


Once again, let’s use 82°F.


(82 – 30) / 2

(52)  / 2



This number is less than two degrees off from the exact answer, and it’s much cleaner to work with.


Fun Fact


Parity is a single point at which the Celsius scale and Fahrenheit scale are equivalent, occuring at -40 degrees. In other words, -40°F equals -40°C!


Here’s the math to prove it:


(-40 x 1.8) + 32

-72 + 32

= -40°


And that’s it—all you need to know about Celsius, Fahrenheit, and switching between the two. Of course, if you have a calculator on hand, we always recommend using the formulas to get an exact conversion value. But if you’re in a pinch, call on the two shortcuts above!


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Short Bio
Rebecca Weinstein is an undergraduate student at Stanford University, where she plans to study English with an emphasis in creative writing. When she is not studying at college, she lives in Morris County, New Jersey with her two dogs and three cats.