Difference Between Fahrenheit and Celsius
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On the Fahrenheit scale, water freezes at
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Difference Between Fahrenheit and Celsius

Hi I'm Adam Kochanowicz for About.com. Did you know there are places in the world where water boils at only 100 degrees? This shouldn't come as any surprise since the United States is only one of very few countries still using the Fahrenheit scale for temperatures.
Information About the Difference Between Fahrenheit and Celsius

If you've ever been overseas or taken a science class, you've probably already encountered some difficulty in understanding the difference between these scales. In this video, I'll tell you what these two scales mean and how to convert between the two.

Fahrenheit was developed in 1724 by physicist Daniel Gabriel Fahrenheit. On this scale, water freezes at 32 degrees and boils at 212 making these points 180 degrees apart. A couple decades later, the Swedish astronmer Anders Celsius defined a new scale after his name which put the freezing and boiling points at 0 and 100 degrees respectively. Pretty much every country in the world excluding the US and Belize replaced Fahrenheit with Celsius in the mid twentieth century. Celsius was also adopted into the Kelvin scale, which uses the same intervals as Celsius but moves zero down to absolute zero, the theoretical coldest temperature physically possible. Kelvin, in turn, was adopted as official scientific unit of temperature. This is why you likely used either Kelvin or Celsius--but never Fahrenheit--in your science classes.

Although we say Fahrenheit and Celsius have boiling and freezing water at different points, it doesn't mean we can simply add or subtract a number to one or the other to convert between the two. Unfortunately, it's much more complicated than that.One degree Fahrenheit is equal to 5/9ths of a degree Celsius. In other words, adding a celsius degree of heat to something makes it hotter than adding a Fahrenheit degree of heat. This ugly 5/9ths fraction makes the conversion a little complicated.
Converting Between Fahrenheit and Celsius

To convert from Fahrenheit to Celsius, subtract 32 and multiply the result by 5/9ths. To convert from Celsius to Fahrenheit, multiply by 9/5ths and add 32.This is the conversion you want to do in a science class. However, if you're just spending some time in Europe and need to know if you'll need a jacket, there are some approximation tricks. First, 5/9ths is pretty close to one half, and 9/5ths is pretty close to two. As long as you're staying in the temperature range of a cold winter and a hot summer, this margin of error is negligible.

For example, if the thermometer at your French hotel reads 36 degrees, multiply not by 9/5ths, but two to get 72. Now add 32 to get 104. In this direction, tell yourself, it's less than 104 degrees Fahrenheit. The actual conversion is 96.8 degrees Fahrenheit. Although 104 is a little hotter than 97 degrees, this quick math will give you a general idea of what to expect. You will not need a jacket when the heat is 97 degrees or a little less than 104 degrees Fahrenheit.An even quicker method is to just memorize certain "landmarks" of temperature in Celsius. You know what 0 and 100 degrees celsius are, so those are your first two landmarks. In terms of your comfort outdoors, Memorize below 4 is cold, 8 degrees is chilly, 15-16 degrees is comfortable, 23 degrees is getting hot, and 42 is unimaginably hot. Now, when you hear the temperature is 20.6 degrees, you'll know it's closer to getting hot than comfortable.