Réaumur to Celsius (°Ré to °C)
1 degree Réaumur equals 1.25 degrees Celsius.
How to convert degrees Réaumur to degrees Celsius
Converting degrees Réaumur to degrees Celsius is not a simple multiplication, so use the formula below.
°C = °Ré × 5/4
Example: 10 degrees Réaumur = 12.5 degrees Celsius.
Temperature scales have different zero points, so converting is not just multiplication. Differences in degrees convert differently from absolute readings.
About these units
Degree Réaumur (°Ré)
A scale proposed in 1730 by René Réaumur in which water freezes at 0° and boils at 80°. Used across Europe until the 19th century and in Russia until the early 20th.
René Antoine Ferchault de Réaumur proposed a thermometer scale in 1730, and it still carries his name. He placed zero at the melting point of water and divided the tube so that each degree was one thousandth of the volume of the bulb and stem below the zero mark. His liquid was diluted alcohol, mixed so that it began to boil after expanding by 8 percent, which gave the familiar 80 degrees for boiling water. The method is also called the octogesimal division.
Instrument makers often filled their tubes with other liquids while still marking 80 for boiling water, which caused real confusion until mercury became nearly universal from the late 18th century, following Jean-André Deluc's tests in 1772. The scale was common in France, Germany and Russia, and appears in the writing of Jefferson, Dostoevsky and Tolstoy. France moved to the centigrade scale in the 1790s, but Réaumur readings lingered in parts of Europe until at least the mid-19th century and in parts of Russia into the early 20th.
Because the interval from freezing to boiling is 80 degrees instead of 100, one degree Réaumur equals 1.25 degrees Celsius, so Celsius is the Réaumur reading times 5/4. Kelvin is that figure plus 273.15. Today the scale survives mainly among some Italian and Swiss cheesemakers, who use it for milk temperatures.
0 degrees Réaumur = 273.15 kelvins (exactly).
Sources: Wikipedia: Réaumur scale
Degree Celsius (°C)
The metric temperature scale used worldwide for weather and daily life: water freezes at 0 °C and boils at 100 °C at standard pressure. Named after Anders Celsius.
Anders Celsius, a Swedish astronomer, proposed a scale in 1742 that ran the opposite way from the one we use: 0 for the boiling point of water and 100 for its freezing point. Credit for flipping it is shared and partly disputed. French physicist Jean-Pierre Christin published a reversed mercury thermometer in 1743, Carl Linnaeus is usually credited with reversing it in 1744, the year Celsius died, and others in Sweden, including Pehr Elvius, Daniel Ekström and Mårten Strömer, are also named as independent developers.
For much of the nineteenth century the scale was called centigrade, until the CGPM and CIPM adopted the name degree Celsius in 1948, partly to honor Celsius and to avoid confusion with a French term for a subdivision of the gradian. From 1954 to 2019 it was defined through absolute zero and the triple point of water; since 2019 it is tied to the Boltzmann constant. Strictly, water boils at about 99.974 degrees on the modern international temperature scale, not exactly 100. Australian weather reports switched exclusively to Celsius in 1972.
0 degrees Celsius = 273.15 kelvins (exactly).
Sources: Wikipedia: Celsius; BIPM: 9th CGPM (1948), Resolution 7; NIST: the kelvin and the SI redefinition
Related conversions
- Celsius to Réaumur (reverse)
- Réaumur to kelvin
- Réaumur to Fahrenheit
- Kelvin to Celsius
- Fahrenheit to Celsius
- Rankine to Celsius
- Delisle to Celsius
- Newton to Celsius
- Rømer to Celsius
See all temperature units.