On the Fahrenheit scale, water boils at 212 degrees and freezes at 32 degrees. On the Celsius scale, it boils at 100 degrees and freezes at 0 degrees. To convert between the two systems, you must perform some basic calculations using the formula (°C × 9/5) + 32 = °F.
- Multiply by nine
The first step is to multiply the Celsius temperature by a factor of nine. If you're beginning with a temperature such as 13 degrees Celsius, in this step, you end up with 117 because you multiply 13 by nine.
- Divide by five
Next, you divide the number from the first step by five. For the example, 117 divided by five equals 23.4. In other words, in the first and second step, you are multiplying by five-ninths. You multiply because the temperature scales up and down at different rates in the two systems.
- Add 32
Finally, you add 32 to the number from the previous step. In the example, 23.4 plus 32 equals 55.4. So 13 degrees Celsius is 55.4 degrees Fahrenheit. You add 32 because the two scales begin at different numbers.
- Reverse the process
If you want to go from Fahrenheit to Celsius, reverse the process. If you start with 55.4, you subtract 32 first, giving you 23.4. Next, you multiply by five to give you 117. Finally, you divide by nine to give you 13 degrees Celsius. The formula is (°F - 32) x 5/9 = °C.