How to convert Celsius to Fahrenheit

Updated June 13, 2017

Your choice of holiday destination may depend on the temperatures you expect to find when you arrive. You can easily tell whether you feel uncomfortably hot or cold, but the two most commonly used temperature scales, developed separately in the 18th century by Daniel Fahrenheit and Anders Celsius, give you objective measurements. Farmers and metereologists were the first to need temperature scales, according to Uppsala University. (See References 1) The Celsius and Fahrenheit scales use different starting numbers and different sizes of division to measure temperature. Both take certain fixed points, the boiling point and freezing point of water, and mark the divisions or degrees between these,

Decide on the method you prefer to use for your calculation. Several sites on the internet, including online, (see References 2) allow you to input your Celsius temperature in one field, before calculating the conversion and giving you the result. You need no mathematical knowledge, or understanding of the scales, to use this method. If you prefer to calculate independently, try using a calculator. Some thermometers offer a Celsius scale on one side of the mercury, and Fahrenheit on the other, to make a calculation unnecessary. Once you understand the formula, you can make the calculation on paper or even in your head.

Multiply your Celsius measurement by 9.

Divide the result by 5, because the scales rise at different rates. Celsius includes 100 degrees between the freezing and boiling points of water. Fahrenheit moves in smaller divisions, using 180 degrees between freezing and boiling points, so multiplying by 180 and dividing by 100 eliminates the difference between the divisions. The fraction 180/ 100 simplifies to 9/5, explains, (see References 3) making the arithmetic easier to perform.

Add 32 to your total because the Fahrenheit scale starts at 32 for the freezing point, while Celsius starts at 0.


For speed, and to avoid undertaking too many calculations, memorise some typical temperatures on both scales. Water boils at 100C and 212F; body temperature is 37C and 98.6F while -40C describes the same extremely cold weather as -40F.

To convert Fahrenheit to Celsius, simply reverse the steps: subtract 32, multiply by 5 and then divide by 9.


Make sure you know which scale you are using. Bath water at 70F is cool, but scalding hot at 70C.

Things You'll Need

  • Temperature in Celsius
  • Internet access, or
  • Calculator, or
  • Pen
  • Paper
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About the Author

Frances Evesham has been writing on communication, language and well-being topics for over 20 years. The author of "Help Your Child To Talk," she has a diploma in speech pathology, is an NLP premier practitioner and is a registered witness intermediary working in the justice system in the U.K.