So, you want to learn how to convert temperature from one temperature scale to another. Apart from going online to use any of the handy temperature conversion tables or formula, you can do it yourself the old school way. With a simple formula or two, you can easily convert temperatures as much as you like.
But, before we get into the nitty-gritty of converting temperature, here are a few things you might want to know.
What we know as the temperature is the amount of energy that matter uses to move its particles. As particles move around, the temperature changes. The more movement there is, the higher the temperature and by contrast, the less movement, the lower the temperature. That is why things get hotter when there is more movement (a simple act of rubbing your hands together (to create friction) also results in a little heat (temperature).
Also, five different scales have been developed to measure how hot or cold things are. These scales are Fahrenheit, Celsius, Kelvin, Rankine, and Réaumur.
We are acquainted with the first two scales since they are used for everyday temperature measurement. The other scales are less popular and are used mainly in scientific circles.
Let’s Take a Closer Look at Each Scale:
Fahrenheit scale –
The Fahrenheit scale was named after Dr. Daniel Gabriel Fahrenheit, a German physicist in 1714. In this scale, negative temperatures (below zero) are included, and the coldest possible temperature on this scale is – 459.67 degrees. The Fahrenheit temperature scale is still used in the United States, while other countries have adopted the metric system which includes the Celsius scale.
• Celsius scale – Did you know that degrees Celsius was initially known as degrees Centigrade? The Celsius temperature scale was later renamed after Dr. Anders Celsius, a Swedish astronomer who had developed it in 1744. The name Celsius was adapted in 1948. Every country other than the United States uses degrees Celsius as the official scale for measuring temperature. This scale sets the freezing point of water at 0 degrees and the boiling point at 100 degrees. Negative temperatures below zero are also included, and the coldest possible temperature (absolute zero) is – 273.15 degrees Celsius.
• Kelvin scale – In 1848 a British scientist, William Thomson (who later became the 1st Baron of Kelvin) developed the Kelvin scale. This scale, which was an adaptation of the existing Celsius scale, is based on the principles of thermodynamics. Not only was the Kelvin scale an alternative to the Fahrenheit and Celsius scales, but it was also to become the preferred scale for scientific measurement and calculations for temperature. One of the main changes introduced by the Kelvin scale was to establish a value for the absolute zero temperature, which is the coldest possible temperature that can be measured. This value was set as zero K (Kelvin does not use degrees in its notation since 1967). Within the Kelvin, scale water freezes at 273.15K, and the boiling point is 373.15K.
• Rankine scale – In 1859, shortly after the Kelvin scale was created, William John Rankine, a Scottish scientist, developed the Rankine scale. It provided an absolute zero value equivalent to what was on the Fahrenheit scale. Like the Kelvin scale, the Rankine scale is also based on the thermodynamic measurement of temperature. In this scale, water freezes at 491.67 °R and reaches its boiling point at 671.67°R. The Rankine scale is not used widely but only in the United States within specific fields of engineering.
• Réaumur scale – Even before the establishment of the Celsius, Kelvin, and Rankine scales, the French developed the Réaumur scale. Named after the French scientist René Antoine Ferchault de Réaumur, this scale established the freezing and boiling points of water at 0 °Re and 80 °Re respectively. The Réaumur scale which at first was widely used in France, Russia and Germany, fell out of widespread usage and was finally restricted to measuring milk temperature in Swiss and Italian cheese factories, and measuring sugar temperature during the making of syrup in the Netherlands.
Temperature Conversion Table
C=5/9 (F-32) F=(9/5C) +32
|TEMPERATURE CONVERSION TABLE|
How to Convert Temperature
Now that you know the various scales used for measuring temperature, let’s learn more about how to convert values from one scale to another. You must use numbers and equations. Of course, there are numerous online applications for doing the different temperature conversions easily.
But, for those who love the challenge of working things out for themselves, here are a few points to note when converting temperature between scales.
1. Learn the freezing and boiling points of water.
Every temperature scale has established the freezing and boiling points of water. Before you can do a temperature conversion, you would need to have an idea of what these are. So, for example, the Fahrenheit scale shows the freezing point of water as 32°F and the boiling point as 212°F. On the other hand, the point at which water freezes on a Celsius scale is 0°C while the boiling point is 100°C.
If you continue with the other scales, you will see that the freezing and boiling points are as follows:
• Kelvin: Freezing 273.15K, Boiling 373.15K
• Rankine: Freezing 491.67°R, Boiling 671.67 °R
• Réaumur: Freezing 0 °Re, Boiling 80 °Re
With the knowledge of the freezing and boiling points, you will also get an idea of the intervals between these points on each scale. So, for example, the Fahrenheit scale has 180 points between the freezing and boiling points, and the Celsius scale has 100 points. The intervals for the Kelvin scale is, therefore, 100 (just like the Celsius scale), for the Rankine scale 180 (just like the Fahrenheit scale). Only the Réaumur has a lower interval of 80 points between freezing and boiling points.
2. Understand the formula
To successfully convert temperature values from one scale to another, you must understand the formula used in each case. Doing so is essential to arrive at the right values and avoid errors that spoil whatever you are doing. Whatever you do to convert from one scale to the next, you must do the exact opposite to reverse the conversion. In the following sections of this article, you will learn how to apply each formula to do the conversions.
3. Have fun
Having fun with temperature conversions may be the last thing you had in mind, but this can help you get over the challenges of numbers and formulae. Once you get the hang of each method, it becomes quite easy to do each conversion. It is fun too. Did you know the temperature of dry ice in Fahrenheit, Celsius, and Kelvin? What about liquid air? Absolute Zero? Here are the answers:
• Dry ice (solid CO₂) is -108 degrees Fahrenheit or -78 degrees Celsius, -200 K.
• Liquid air is -312 degrees Fahrenheit or -191 degrees Celsius, -100K,
• Absolute zero (the coldest possible measurable temperature) is -459 degrees Fahrenheit or -273 degrees Celsius, -0K.
Types of Temperature Conversation
Let’s talk about the different types of temperature conversion. To understand them, consider the five scales used to measure temperature. As you have learned, these are the popular Fahrenheit and Celsius, and the less widely used scales – Kelvin, Rankine, and Réaumur.
Each scale is, of course, different. The main difference among these scales is the freezing and boiling points of water as you have seen earlier.
Of course, with five different temperature scales to work with, there are multiple ways to convert temperature from one scale to the next. So, you have conversion from Fahrenheit to Celsius, Fahrenheit to Kelvin, Fahrenheit to Rankine, and Fahrenheit to Réaumur. You can also convert them back to Fahrenheit. The same principle applies when for converting Celsius to Fahrenheit, Kelvin, Rankine, and Réaumur.
You get the idea:
Converting from Kelvin to the other scales and back again is entirely possible. Converting from Rankine to the other scales, as well as converting from Réaumur to the different scales is also possible. To do so, you would need to use the relevant formula and equations.
Let’s look at these formulae and equations in the next sections.
Temperature conversion formula
To convert from degrees Fahrenheit to degrees Celsius, take 32 from the Fahrenheit temperature then multiply by .5556 (or 100/180 simplified as 5/9). Stated another way, deduct 32, multiply by 5, finally, divide by 9.
That’s it! Easy peasy.
Here is an example of how this formula works:
40°F – 32 x .5556 = 4.5°C
Put another way, here is the example again.
40°F – 32 = 8
8 x .5556 = 4.5°C
Was that clear? Would you be able to convert Degrees Fahrenheit to Degrees Celsius on your own?
Using the fractions in your calculation, here is an example to convert Fahrenheit to Celsius:
First: 90° − 32 = 58
Then: (58 × 5) / 9 = 290/ 9 = 32.2° C
Let’s now look at converting degrees Celsius to degrees Fahrenheit.
What do you think we need to do in this case? Do the reverse of what was done to convert °F to °C. Multiply the degrees Celsius by 1.8 (or 180/100 simplified as 9/5) then add 32. Expressed another way, multiply by 9, divide by 5, finally add 32.
That’s all. There is nothing to it.
Here is an example: 50°C x 1.8 + 32 = 122°F
Or, shown as two steps:
50°C x 1.8 = 90
90 + 32 = 122°F
Using the fractions in your calculations here is an example to convert Celsius to Fahrenheit:
First: (30° × 9) / 5 = 270/5 = 54
Then: 54 + 32 = 86° F
You have seen the formula most commonly used to convert Fahrenheit to Celsius and vice versa. There are, however, other formulae that you can apply to get the same or similar results when converting between Fahrenheit and Celsius.
The first one is to add 40, then multiply the values, followed by subtracting 40. The reason for using 40 in this calculation is that this is where both Fahrenheit and Celsius are equal. That is −40° C is equal to −40° F.
So, to convert Fahrenheit to Celsius using 40 in the calculations, first add 40 to the Fahrenheit value (for example 40 degrees) The sum is 80. Next, multiply by 5/9 or .5556 to get 44.45. Finally, subtract 40 to get 4.45. As you can see from the earlier example using the previous conversion formula, this result is very close.
To convert Celsius to Fahrenheit using 40 in your calculation will be just as easy. In this example, you are turning 50 degrees Celsius to Fahrenheit (as you have done in the previous case using the other formula).
First, add 40 to 50 to get 90. Then multiply 90 by 9/5 or 1.8 to reach 162. Finally, subtract 40 to reach 122°F. Again, as you can see, the result in this example is the same as the one arrived at when you used the formula 50°C x 1.8 + 32.
You can use other formulas to estimate temperatures quickly. So, to convert from °C to °F, multiply the value by 2, then add 30. For °F to °C conversion, subtract 30 then divide by 2. Remember that the results you get when you use this approach will not be the same as your results using the other equations. This formula is handy when you want to get a quick temperature conversion (such as when cooking).
Here are the formulae you will need for conversions to and from Kelvin, Rankine, and Réaumur.
Conversion to Kelvin
• From Fahrenheit: Subtract 32 from the temperature in Fahrenheit, multiply by 5, then divide by 9 (alternately, multiply by .5556), finally subtract 273.15.
• From Celsius: Add 273.15 to the temperature in Celsius to get the temperature in Kelvin.
• From Rankine: Subtract 764.84 from the temperature in Rankine, then multiply the result by 5, finally divide by 9 (alternatively, multiply the result by .5556).
• From Réaumur: Multiply the temperature in Réaumur by 10, divide the result by 8 (alternatively multiply by 1.25), finally add 273.15.
Conversion from Kelvin
• To Fahrenheit: Subtract 273.15 from the temperature in Kelvin, multiply by 9, then divide by 5 (alternately, multiply by 1.8), finally add 32.
• To Celsius: Subtract 273.15 from the temperature in Kelvin to get the temperature in Celsius.
• To Rankine: Multiply the temperature in Kelvin by 9, then divide by 5 (alternatively, multiply by 1.8), finally add 764.84.
• To Réaumur: Subtract 273.15 from the temperature in Kelvin, then multiply by 0.8 (or 4/5).
Conversion to Rankine
• From Fahrenheit: Add 459.69 to the temperature in Fahrenheit to get the temperature in Rankine.
• From Celsius: Multiply the temperature in Celsius by 9, divide the result by 5 (alternatively multiply °C by 1.8), then add 491.69.
• From Kelvin: Add 764.84 to the temperature in Kelvin, then multiply the result by 9, finally divide by 5 (alternatively, multiply the result by 1.8).
• From Réaumur: Multiply the temperature in Re by 9, divide the result by 4 (alternatively multiply by 2.25), add 32, finally add 459.67 (alternatively you may add 491.67 in one step).
Conversion from Rankine
• To Fahrenheit: Subtract 459.69 from the temperature in Rankine to get the temperature in Fahrenheit.
• To Celsius: Subtract 491.69 from the temperature in Rankine, multiply the result by 5, then divide by 9 (alternatively multiply the result by .5556).
• To Kelvin: Subtract 764.84 from the temperature in Rankine, then multiply the result by 5, finally divide by 9 (alternatively, multiply the result by .5556).
• To Réaumur: Subtract 32 from the temperature in Rankine, subtract 459.67 from the result (alternatively you may subtract 32+459.67 or 491.67 in one step), then multiply the result 9, divide the result by 4 (alternatively divide the result by 2.25).
Conversion to Réaumur
• From Fahrenheit: Subtract 32 from the temperature in Fahrenheit, multiply the result by 9, then divide by 4 (alternatively divide the result by 2.25).
• From Celsius: Multiply the temperature in Celsius by 4, divide the result by 5 (alternatively multiply °C by 0.8). That’s it!
• From Kelvin: Subtract 273.15 from to the temperature in Kelvin, then multiply the result by 4, finally divide by 5 (alternatively, multiply the result by 0.8).
• From Rankine: Subtract 32 from the temperature in Rankine, then subtract 459.67 (alternatively, you may subtract 491.67 in one step), multiply the result by 9, divide by 4 (alternatively you may divide the result by 2.25).
Conversion from Réaumur
• To Fahrenheit: Multiply the temperature in Réaumur by 9, then divide by 4 (alternatively multiply the temperature in Réaumur by 2.25), finally, add 32.
• To Celsius: Multiply the temperature in Réaumur by 10, divide by 8 (alternatively multiply the temperature in Réaumur by 1.25).
• To Kelvin: Multiply the temperature in Réaumur by 10, divide by 8 (alternatively multiply the temperature in Réaumur by 1.25). Finally, add 273.15.
• To Rankine: Multiply the temperature in Réaumur by 9, divide by 4 (alternatively multiply the temperature in Réaumur by 2.25), add 32, finally, add 459.67 to the result (alternatively you may add 491.67 in one step).
Temperature conversion equation
Equations also express the steps needed to convert temperature from one scale to the other. They are your quick reference whenever you need them.
Convert from Fahrenheit to the other scales:
• To Celsius: (F – 32) / 1.8 = °C
• To Kelvin: (F + 459.67) / 1.8 = K
• To Rankine: F + 459.67 = °Ra
• To Réaumur: (F – 32) / 2.25 = °Re
Convert from Celsius:
• To Fahrenheit: (C × 1.8 + 32) = °F
• To Kelvin: C+ 273.15 = K
• To Rankine: C × 1.8 + 32 + 459.67 = °Ra
• To Réaumur: C × 0.8 = °Re
Convert from Kelvin:
• To Fahrenheit: K × 1.8 – 459.67 = °F
• To Celsius: K – 273.15 = °C
• To Rankine: K × 1.8 = °Ra
• To Réaumur: (K – 273.15) × 0.8 = °Re
Convert from Rankine:
• To Fahrenheit: Ra – 459.67 = °F
• To Celsius: (Ra – 32 – 459.67) / 1.8 = °C
• To Kelvin: Ra / 1.8 = K
• To Réaumur: (Ra – 32 – 459.67) / 2.25 = °Re
Convert from Réaumur:
• To Fahrenheit: Re × 2.25 + 32 = °F
• To Celsius: Re × 1.25 = °C
• To Kelvin: Re × 1.25 + 273.15 = K
• To Rankine: Re × 2.25 + 32 + 459.67 = °Ra
You might be familiar with the two main temperature scales – Fahrenheit and Celsius – of the five scales developed to measure how hot or cold things are. The formulas and equations connected to each scale are used when converting temperature values. They are easy and fun to use for your conversions. Use them as a reference whenever you need to.