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What’s Fahrenheit?

By David, 15 August 2017 Activity

A thermometer with both Celsius and Fahrenheit measurements.

Image: ©iStock.com/ MarianVejcik

Do you have friends from the United States? Have you ever found a recipe on the internet with ridiculously high oven temperatures? Do you have a grandparent (or great grandparent) who doesn’t like the ‘new’ way of measuring temperatures? You might need our quick guide to the Fahrenheit scale.

First, some quick notation. Temperatures in Fahrenheit are noted with °F. Those in the regular, Celsius scale are written with °C.

Important temperatures

  • 32 °F : water freezes
  • 98 °F : normal body temperature
  • 212 °F : water boils
  • 356 °F : a moderate oven temperature for baking
  • –40 °F : the same temperature as –40 °C

Turning Celsius into Fahrenheit

  1. Start with a Celsius temperature.
  2. Multiply by 2.
  3. Take the first digit, and subtract it from your number. If it’s more than 100, read off the first two digits as a two digit number, and subtract that instead.
  4. Add 32.
  5. That’s it! Your number should be close to the temperature in Fahrenheit.

Turning Fahrenheit into Celsius

  1. Subtract 32.
  2. Take the first digit and add it to your number. If it’s bigger than 100, take the first two digits as one number and add that instead.
  3. Divide by 2.
  4. That’s it! Your number should be close to the temperature in Celsius.

What’s happening?

Fahrenheit is a very old temperature scale, invented almost 300 years ago by a Dutch scientist named Daniel Fahrenheit. There are many stories about how Fahrenheit decided to number his scale. In a letter, he explained that zero degrees was the temperature where very salty water froze. He also wanted to have 64 degrees between ice melting and body temperature, because it was easy to mark out 64 even spaces on his thermometers!

These days, almost every country in the world uses Celsius. Only the United States, the Bahamas, Belize, and the Cayman Islands use Fahrenheit as their main temperature scale. But many scientists use a third scale, known as Kelvin (K). Just like with Celsius, there are 100 Kelvin degrees between water freezing and boiling. The difference is that Kelvin starts counting from absolute zero, which is –273 °C. In the Kelvin scale, water freezes at 273 K and boils at 373 K.

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