Reaumur to Celsius
°Ré
°C
Conversion History
| Conversion | Reuse | Delete |
|---|---|---|
| No conversion history to show. | ||
Quick Reference Table (Reaumur to Celsius)
| Reaumur (°Ré) | Celsius (°C) |
|---|---|
| 0 | 0 |
| 16 | 20 |
| 29.6 | 37 |
| 60 | 75 |
| 80 | 100 |
About Reaumur (°Ré)
The Réaumur scale (°Ré) is a historical temperature scale proposed by French scientist René Antoine Ferchault de Réaumur in 1730. It sets 0°Ré at the freezing point of water and 80°Ré at the boiling point. Réaumur divided the interval into 80 parts because he calibrated it using a dilute alcohol thermometer whose fluid expanded by 80 parts in volume between these two reference points. The scale was widely used in France, Germany, and Russia throughout the 18th and early 19th centuries before being replaced by Celsius. A vestigial use survives in confectionery, where some older European recipes specify sugar syrup temperatures in Réaumur degrees.
Body temperature (37°C) is approximately 29.6°Ré. A comfortable room at 20°C is 16°Ré. Boiling water is 80°Ré.
Etymology: Named after René Antoine Ferchault de Réaumur (1683–1757), a French polymath best known for his multi-volume work on insect natural history. He developed the scale in 1730 using dilute alcohol (roughly 80% water, 20% alcohol) whose measured volumetric expansion between freezing and boiling defined the 80-degree interval.
About Celsius (°C)
Celsius (°C) is the most widely used temperature scale in the world, adopted by every country except the United States, Liberia, and Myanmar for everyday and scientific use. Zero degrees Celsius is defined as the freezing point of water at standard atmospheric pressure; 100°C is the boiling point. Originally called centigrade because of its 100-degree span between these two reference points, it was renamed Celsius in 1948 to honor Swedish astronomer Anders Celsius. It is the practical temperature scale for weather, cooking, medicine, and most scientific work outside thermodynamics. Body temperature is 37°C; a comfortable room is typically 20–22°C.
Water freezes at 0°C and boils at 100°C. Normal human body temperature is 37°C. A warm summer day in southern Europe is around 35°C.
Etymology: Named after Swedish astronomer Anders Celsius (1701–1744), who proposed a 100-degree scale in 1742. His original scale was inverted — 0°C meant boiling, 100°C meant freezing — and was reversed by fellow Swede Carl Linnaeus shortly after his death.
Reaumur – Frequently Asked Questions
Who invented the Réaumur scale?
The Réaumur scale was proposed by René Antoine Ferchault de Réaumur in 1730. Réaumur was a French scientist primarily known for his contributions to natural history, particularly entomology. His thermometer used dilute alcohol and was calibrated between the freezing and boiling points of water, with the scale divided according to the actual expansion of the alcohol.
Why does the Réaumur scale go from 0 to 80?
Réaumur calibrated his scale based on the physical expansion of his thermometric fluid — a specific dilute alcohol mixture. Between water's freezing and boiling points, the fluid expanded by exactly 80 parts in 1000 of its volume at freezing. He used this empirical measurement directly as the degree count, making 80°Ré the boiling point. The number 80 was not chosen arbitrarily but measured.
Why did France abandon Réaumur in favor of Celsius?
The French Revolution's embrace of the metric system in the 1790s demanded decimal-friendly units. Celsius's 0-to-100 scale fit the decimal philosophy perfectly; Réaumur's 0-to-80 did not. The French Academy of Sciences standardized Celsius for scientific work, and it spread through Napoleonic Europe. Réaumur lingered in German-speaking regions and Russia into the mid-19th century but eventually yielded everywhere. The irony is that Réaumur was French — his own country was the first to abandon his scale.
How do you convert Réaumur to Celsius?
Multiply the Réaumur value by 5/4 (or 1.25). For example, 16°Ré × 1.25 = 20°C. To convert Celsius to Réaumur, multiply by 4/5 (or 0.8). The two scales share the same zero (0°C = 0°Ré); they differ only in degree size, since 100°C = 80°Ré.
How did sugar confectioners use Réaumur degrees in candy-making?
Classic French confectionery texts list sugar syrup stages in Réaumur: "thread" stage at 80°Ré (100°C), "soft ball" at 94°Ré (117°C), "hard crack" at 124°Ré (155°C). Pastry chefs memorized these benchmarks and tested with a thermometer or by dripping syrup into cold water. Some vintage French and Swiss recipe books still reference Réaumur temperatures — modern reprints add Celsius equivalents in brackets. It is the last practical domain where Réaumur had a lingering foothold.
Celsius – Frequently Asked Questions
Which countries use Celsius?
Almost every country in the world uses Celsius for everyday temperatures — weather forecasts, cooking, and body temperature. The United States, Liberia, and Myanmar are the principal exceptions, using Fahrenheit for daily life, though US scientists use Celsius for research.
What is absolute zero in Celsius?
Absolute zero — the theoretical minimum temperature where molecular motion effectively ceases — is −273.15°C. This corresponds to 0 K on the kelvin scale. It is not physically achievable but has been approached to within a few billionths of a degree in laboratory conditions.
How do you convert Celsius to Fahrenheit?
Multiply the Celsius value by 9/5 (or 1.8) and add 32. For example, 20°C × 1.8 + 32 = 68°F. A quick mental approximation: double the Celsius value and add 30 (gives ±2°F accuracy for typical weather temperatures).
What is normal body temperature in Celsius?
Normal human body temperature is approximately 37.0°C (98.6°F), though it varies by individual, time of day, and measurement site. A temperature above 38.0°C is generally considered a fever; hypothermia is diagnosed below 35.0°C.
What is the difference between Celsius and centigrade?
Centigrade is the old name for the same scale — both refer to a 100-degree span between water's freezing and boiling points ("centi" = 100, "grade" = step). The name was officially changed to Celsius in 1948 to avoid confusion with the angular unit also called "grade" (or "gradian") in some languages.