Temperature is typically measured in Celsius units in the metric system and Fahrenheit in the English system. There are, however, many other temperature scales. It is helpful to become familiar with each one.
The Celsius temperature scale was named after a Swedish astronomer Anders Celsius. On the Celsius scale, the boiling point of water (at normal atmospheric pressure) is 100 degrees and the freezing point of water is 0 degrees. The symbol for a degree of Celsius is "C."
The Fahrenheit scale was named after German physicist Gabriel Fahrenheit, who proposed the scale in 1724. In the Fahrenheit scale, the freezing point of water is 32 degrees and the boiling point is 212 degrees. The symbol is "F."
The Réaumur scale, not commonly known, was named after French scientist René Antoine Ferchault de Réaumur. He set the freezing point at 0 degrees and the boiling point at 80 degrees. The scale is not often used. The symbol is "Re."
The Kelvin scale was named after William Thomson, 1st Lord Kelvin, a Scottish mathematician and physicist. He worked with other scientists to produce an absolute scale of temperature based on laws of heat rather than the freezing and boiling points of water. His work produced the idea of 'absolute zero,' the temperature at which all matter ceases motion. It is impossible for anything to be colder than absolute zero, or 0 degrees Kelvin (-273 degrees on the Celsius scale). The symbol is "K."
William J.M. Rankine, a Scottish engineer and physicist, promoted a similar scale, the Rankine scale. It measures absolute zero in terms of degrees Fahrenheit (-459.67 degrees Fahrenheit). The symbol is "ºR."