The formula for converting degrees Celsius to degrees Fahrenheit is

F = 9/5 C + 32

So it is customary to multiply the Celsius value by 9 and divide it by 5 before adding 32 to the result. A little manipulation of the formula will make it suitable to mental calculation. The decimal equivalent of 9/5 is 1.8 which is simply 2 – 0.2. So a more user friendly form of the conversion is

F = 9/5 C + 32 = 1.8 C + 32 =  (2 – 0.2)C + 32

This short cut can be better understood if we take simple examples:

Example 1: 45^oC = 113^oF

a)      Double the Celsius value 45 to get 2C: 45 x 2 = 90;

b)      Move the decimal point of 2C one place to the left to get 0.2C: 90 x 0.1=9.0

c)       Subtract 0.2C from 2C : 90 – 9 = 81

d)      Add 32 to the result :81 + 32 = 113

Example 2: 37^oC

a)      2C = 2 x 37 = 74

b)      0.2 C = 74 x 0.1 = 7.4

c)       2C – 0.2C = 74 – 7.4 = 66.6

(2C- 0.2C) + 32 = 98.6^oF

Celsius to Fahrenheit conversion, made easy, with a MATH-Inic short cut!