When I'm talking to coworkers in Canada from our office in Texas, the weather is a common topic. Whether I want to complain about 100-degree summer days or they want to brag about a temperature of 25, it's a good idea for us to convert the temperature into the other person's units.

While Canada uses the metric system that gives temperatures in degrees Celsius, the United States is one of a few countries that still uses degrees Fahrenheit. The different temperature scales mean that while I might find myself shivering at 25°F (degrees Fahrenheit), my Canadian pals would be quite comfy at 25°C (degrees Celsius). That's because that temperature works out to a balmy 77°F.

Different temperature scales
Credit: renaissancechambara / Flickr.com

Easy formulas for converting between Celsius and Fahrenheit

So how do you convert between the two? There are two simple formulas:

To convert °C to °F

F = (9/5 C) + 32

  1. divide the Celsius temperature by 5
  2. multiply the answer by 9
  3. add 32 to the result

Example, 15°C = 59°F   (15 / 5 = 3,  3 * 9 = 27,  27+32 = 59)

 

To convert °F to °C

C = 5/9 (F-32)

  1. subtract 32 from the Fahrenheit temperature
  2. divide the answer by 9
  3. multiply the result by 5

Example, 104°F = 40°C  (104-32 = 72, 72/9 = 8, 8*5 = 40)


This method works for any Celsius or Fahrenheit temperature.

Why does this work?

Celsius temperatures are based on the freezing and boiling points of water: 0°C is the freezing point and 100°C is the boiling point. Compare those to the somewhat illogical values for the same points in Fahrenheit, 32°F and 212°F.

If you look at the numbers for a while, you can see that the difference between boiling and freezing points is 100 degrees in Celsius and 180 degrees in Fahrenheit. So each Fahrenheit degree is 100/180 Celsius degrees, or 5/9 of a degree. Now, all you need to do is get the two scales starting at the same point. If you could subtract 32 from the Fahrenheit scale, both scales would start at zero. That's the basis of the conversion from Fahrenheit to Celsius: subtract 32 so the scales match at zero, and then add 5/9 of a degree to the Celsius temperature for every degree of the Fahrenheit temperature.