How to Convert Negative Celsius to Fahrenheit

By Jon Zamboni
Celsius and Fahrenheit use different formulas.

Both the Celsius and Fahrenheit scales include temperatures that are below zero degrees. However, the 0 degree point on the two scales do not line up on a 1-to-1 ratio, so some temperatures are negative in Celsius but positive in Fahrenheit.

How Do Fahrenheit and Celsius Match Up?

On the Celsius scale, water freezes at 0 degrees -- in Fahrenheit, water freezes at 32 degrees. Because of this, all temperatures between 0 and 32 degrees Fahrenheit are positive on the Fahrenheit scale and negative in Celsius. Zero degrees Fahrenheit lines up with -17.778 degrees Celsius, so all temperatures below -17.778 degrees Celsius are negative in both Celsius and Fahrenheit. Also, at -40 degrees Celsius and Fahrenheit the temperatures match up. So, -40 degrees Celsius and -40 degrees Fahrenheit are the same temperature.

Converting From Celsius to Fahrenheit

To convert from degrees Celsius – C -- to degrees Fahrenheit – F -- use the following equation:

F = 1.8 x C + 32

So, to convert a temperature from Celsius to Fahrenheit, you multiply it by 1.8, then add 32. Say you want to find what -10 degrees C is in Fahrenheit. First, multiply -10 by 1.8. Remember that a negative number multiplied by a positive number is a negative number.

-10 x 1.8 = -18

Add 32 to -18 to get the temperature in Fahrenheit:

-18 + 32 = 14

So, -10 degrees C is 14 degrees F.

Convert From Fahrenheit to Celsius

You can also convert a negative Fahrenheit temperature to a Celsius temperature.

To convert Fahrenheit to Celsius, use the following formula:

C = (F - 32)/1.8

For instance, if you wanted to convert -45 degrees Fahrenheit to Celsius, first subtract 32 from 45. This results in in -77. Then, divide 77 by 1.8:

C = -77/1.8 C = 42.78

So, -45 degrees Fahrenheit are -42.78 degrees Celsius.

About the Author

Jon Zamboni began writing professionally in 2010. He has previously written for The Spiritual Herald, an urban health care and religious issues newspaper based in New York City, and online music magazine eBurban. Zamboni has a Bachelor of Arts in religious studies from Wesleyan University.