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Conversion of Centigrade (Celsius) Fahrenheit Temperature

Electricians select conductors and other equipment based on the temperature where they are to be installed. There are times when one temperature scale needs to be converted to the other. Here is the calculator technique to accomplish this conversion:

In the formulas below, / represents division, * represents multiplication, - subtraction, + addition and = is equal.

Tc = (5/9)*(Tf-32); Tc = temperature in degrees Celsius, Tf = temperature in degrees Fahrenheit

For example, suppose you have a Fahrenheit temperature of 98.6 degrees and you wanted to convert it into degrees on the Celsius scale. Using the above formula, you would first subtract 32 from the Fahrenheit temperature and get 66.6 as a result. Then you multiply 66.6 by five-ninths and get the converted value of 37 degrees Celsius.

Below is the formula to convert a Celsius scale temperature into degrees on the Fahrenheit scale.

Tf = (9/5)*Tc+32; Tc = temperature in degrees Celsius, Tf = temperature in degrees Fahrenheit

Assume that you have a Celsius scale temperature of 100 degrees and you wish to convert it into degrees on the Fahrenheit scale. Using the stated formula, you first multiply the Celsius scale temperature reading by nine-fifths and get a result of 180. Then add 32 to 180 and get the final converted result of 212 degrees on the Fahrenheit scale.

Below is another accepted conversion method that works just as well and perhaps might be easier to remember. No matter which direction you want go, from Fahrenheit to Celsius or Celsius to Fahrenheit, always first add 40 to the number. Next, multiply by 5/9 or 9/5 just like the first method. Then, always subtract out the 40 you just added to yield the final result. To remember whether to use 5/9 or 9/5 when converting from Fahrenheit to Celsius or Celsius to Fahrenheit, just simply remember, F (for Fahrenheit) begins with the same letter as Fraction. 5/9 is always a Fraction; while 9/5 is also a fraction, in this form, it is Clearly a whole number plus a fraction (1 and 4/5). Thus, if you want to convert Fahrenheit (F) to Celsius (C), then use the Fraction 5/9; Celsius (C) to Fahrenheit (F), use the other, 9/5, which is Clearly not just a fraction.

For an example of this method, we'll use the values we used in the initial example, 98.6 F and 37 C, which are equal.

To convert from F to C, try these calculations manually.
98.6 + 40 = 138.6, and 138.6 * 5/9 = 77. For the final calculation, remove the 40. 77 - 40 = 37

To convert from C to F, try these calculations manually.
37 + 40 = 77, and 77 * 9/5 = 138.6. For the final calculation, remove the 40. 138.6 - 40 = 98.6

In summary, add 40, (F to C) multiply by Fraction...(C to F) multiply by the other, subtract 40.

The Celsius temperature scale is still sometimes referred to as the "centigrade" scale. Centigrade means "consisting of or divided into 100 degrees;" the Celsius scale, devised by Swedish Astronomer Andres Celsius (1701-1744) for scientific purposes, has 100 degrees between the freezing point (0 C) and boiling point (100 C) of pure water at sea level air pressure. The term Celsius was adopted in 1948 by an international conference on weights and measures.

Here is a chart which makes calculations unnecessary unless extreme accuracy is important.


-40 deg. -40 deg.
-17.8 deg. 0 deg.
- 10 deg. 14 deg.
0 deg. 32 deg.
5 deg. 41 deg.
10 deg 50 deg.
15 deg. 59 deg.
20 deg. 68 deg.
25 deg. 77 deg.
30 deg. 86 deg.
35 deg. 95 deg.
40 deg. 104 deg.
50 deg. 122 deg.
60 deg. 140 deg.
70 deg. 158 deg.
80 deg. 176 deg.
90 deg. 194 deg.
100 deg. 212 deg.


Conversion from one temperature scale Celsius (Centigrade) to Fahrenheit, or back, is not a task an electrician typically performs. But it is included here as a type of calculator practice problem.

If you know Centigrade degrees C and want to find Fahrenheit degrees F, here is he formula:\

    degrees F = 9/5 degrees C + 32

On the calculator:

Clear 9 / 5 x degrees C = + 32 = read answer

If you want Fahrenheit degrees F and want to find Centigrade degrees C, here is the formula:

    degrees C = 5/9 (F - 32)

On the calculator:

Clear 5 / 9 x ( degrees F - 32) = read answer

Where a parenthesis occurs in a formula, ( or ), pay attention to if it is a left ( or a right ) parenthesis. There are even times when making electrical calculations where more than one set of parenthesis are included in a formula. Just enter then as you come to them. Let the calculator worry about keeping them straight.

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