How Do I Convert Temperatures?

Question: I heard recently that the temperatures in parts of Canada were 20 degree Celsius below normal. When I converted that to the Fahrenheit scale using my calculator, I got temperatures that were 68 degrees below normal. This does not sound right. What did I do wrong?

Answer: This is a very common mistake. You see there is a subtle difference between degrees Celsius (or degrees Fahrenheit) and Celsius degrees (or Fahrenheit degrees ). Most calculators only calculate the first conversion.

What is that difference? Well, degrees Celsius or degrees Fahrenheit are what you read on a thermometer scale. Celsius degrees or Fahrenheit degrees are the intervals between the gradations on that thermometer scale. When we talk about temperature readings, we are actually referring to degrees Celsius or degrees Fahrenheit. But when we talk about differences between two temperatures, we should use Celsius degrees or Fahrenheit degrees.

The degree in the Celsius scale is larger than the Fahrenheit equivalent. The conversion is Celsius times 1.8 equals Fahrenheit. Thus a one Celsius degree rise in temperature is equivalent to a 1.8 Fahrenheit degree rise. Your 20 Celsius degree temperature difference is in fact 36 Fahrenheit degree difference, not 68.

When you convert absolute temperatures, you must account for the difference in the zero points. Thus to convert degrees Celsius to degrees Fahrenheit, multiply the degrees Celsius by 1.8 and add 32.

Now, if the normal temperature for the region in question was 4 degrees Celsius and the weather was 20 Celsius degrees below normal, that would convert to a normal of 39 degrees Fahrenheit with the weather 36 Fahrenheit degrees below normal.

Weathercasters, the media and many meteorologists are sloppy about the terminology often dropping the degree notation or calling everything degrees whatever. In fact, the degree mark should be after the letter when we talk of Celsius degrees, that is C° compared to °C, which denotes degrees Celsius.

Learn More From These Books Chosen by The Weather Doctor

• Williams, Jack: The Weather Book, 1997, Vintage Books, ISBN 0-679-77665-6.
• Dunlop, Storm: The Weather Identification Handbook: The Ultimate Guide for Weather Watchers,, 2003, The Lyons Press, ISBN 1585748579. (pb).

The Weather Doctor's Weather Almanac How Do I Convert Temperatures?
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