Formula for Fahrenheit and Celsius Conversions

Celsius thermometer
Celsius thermometer. (Petr Kratochvil/publicdomainpictures.net)

Although there are many online temperature converters, it's always helpful to have a knowledge of the actual formula for the conversions.

C is Celsius

F is Fahrenheit

C = 5/9 (F-32)

F = 9/5 (C+32)

Let's try converting 68 degrees Fahrenheit to celsius 5/9(68-32)

Step 1: 68 less 32 is 36

Step 2: 5 divided by 9 is 0.5555555555555

Step 3: Multiply the repeating decimal by 36

Step 4: Your solution is 20

Now, convert 20 degrees Celsius to Fahrenheit to check your work.

9/5C +32

Step 1: 9 divided by 5 is 1.8

Step 2: 1.8 multiplied by 20 is 36

Step 3: 36 plus 32 = 68

So you need to have some strategies to make the conversion in your head?

Method 1 -  C to F -  Double Less 10% Add 32

This works quite well for many people. 

Consider this report: The temp today is 18 C. Being used to Fahrenheit, you need to convert to know what to wear outside. So double the 18 ( 2 x 18) = 36. 10 % of 36 is 3.6 - round to 4.

36 -4 = 32. 32 add 32 = 64. So I will bring a sweater but not a big coat. 

Try this one in your head: 29 C.  

Solution: 84 F. 

29 doubled = 58. 

10 % of 58 = 5.8, round to 6.

58 - 6 = 52.

52 add 32 = 84.

So a nice warm day!

Method 2 - C to F or F to C.  Memorize Your 10 Blocks

If accuracy is not critical, memorize the 10's and work with the range.

10 C = 52 F

20 C = 68 F

30 C =86 F

40 C = 104 F

So you are told the temp is 15 C. The range is 52 to 68 and the middle is 60 F.

For weather, 20 C is nice but 30 C is very nice.

Wouldn't it be nice if we just had one system for measurement?!