A hundred degrees tomorrow

About this video

When someone in the United States says it will be 100 degrees tomorrow, they mean a very hot summer day, not boiling water. They are using the Fahrenheit scale. Most of the world uses Celsius, where 100 degrees is the temperature at which water boils.

This animation puts the two thermometer scales side by side. Water freezes at 0 °C, which is 32 °F, and boils at 100 °C, which is 212 °F. So between freezing and boiling, Celsius has 100 steps and Fahrenheit has 180 smaller ones: a Fahrenheit degree is a little more than half a Celsius degree. To convert Celsius to Fahrenheit in your head, double the number and add 30. A mild 20 °C day comes out at about 70 °F; the exact answer is 68 °F, from °F = °C × 1.8 + 32.

Transcript

1. 0:00It's going to be 100 degrees tomorrow! Is the city about to boil?
2. 0:05No. In Fahrenheit, 100 degrees is just a very hot day.
3. 0:10Water boils at 100 Celsius, which is 212 Fahrenheit.
4. 0:14It freezes at 0 Celsius: 32 Fahrenheit.
5. 0:17Between them, Celsius counts 100 steps. Fahrenheit counts 180 smaller ones.
6. 0:22A rough rule to convert: double the Celsius number, then add 30. Twenty becomes 70; exactly, it's 68.
7. 0:30Same heat. Different marks.