Difference Between Celsius and Centigrade

Depending on how old you are, you might read 38°C as 38 degrees Celsius or 38 degrees centigrade. Why are there two names for °C and what's the difference? Here's the answer:

Celsius and centigrade are two names for essentially the same temperature scale (with slight differences). The centigrade scale is divided into degrees based on dividing the temperature between which water freezes and boils into 100 equal gradients or degrees. The word centigrade comes from "centi-" for 100 and "grade" for gradients. The centigrade scale was introduced in 1744 and remained the primary scale of temperature until 1948. In 1948 the CGPM (Conference General des Poids et Measures) decided to standardize several units of measurement, including the temperature scale. Since the "grade" was in use as a unit (including the "centigrade"), a new name was chosen for the temperature scale: Celsius.

The Celsius scale remains a centigrade scale in which there are 100 degrees from the freezing point (0°C) and boiling point (100°C) of water, though the size of the degree has been more precisely defined. A degree Celsius (or a Kelvin) is what you get when divide the thermodynamic range between absolute zero and the triple point of a specific type of water into 273.16 equal parts. There is a 0.01°C difference between the triple point of water and the freezing point of water at standard pressure.

The temperature scale created by Anders Celsius in 1742 was actually the reverse of the modern Celsius scale. Celsius' original scale had water boil at 0 degrees and freeze at 100 degrees. Jean-Pierre Christin independently proposed at a temperature scale with zero at the freezing point of water and 100 was the boiling point (1743). Celsius' original scale was reversed by Carolus Linnaeus in 1744, the year in which Celsius died.

The centigrade scale was confusing because "centigrade" was also the Spanish and French term for a unit of angular measurement equal to 1/100 of a right angle. When the scale was extended from 0 to 100 degrees for temperature, centigrade was more properly hectograde. The public was largely unaffected by the confusion. Even though the degree Celsius was adopted by international committees in 1948, weather forecasts issued by the BBC continued to use degrees centigrade until February 1985!