Convert Réaumur to Celsius
Convert degrees réaumur to degrees celsius instantly. 1 °Ré = 1.25 °C — use the live calculator, the exact formula, a reference-temperature table and worked examples. Also check the Celsius to Réaumur converter for the reverse conversion.
Units explained
Réaumur
The degree Réaumur (°Ré) sets the freezing point of water at 0 °Ré and the boiling point at 80 °Ré, so one degree Réaumur equals exactly 1.25 kelvins (5/4 K).
Devised by French scientist René Antoine Ferchault de Réaumur using alcohol thermometers whose working liquid expanded 80 parts per thousand between the freezing and boiling points of water — the origin of the 80-degree span.
Once dominant across 18th- and 19th-century Europe, especially France, Germany, and Russia. It survives today mainly in traditional cheese-making — Parmigiano-Reggiano and Swiss alpine dairies still specify milk temperatures in °Ré.
Introduced by Réaumur in Paris in 1730; it faded from general use after France adopted the Celsius scale with the metric system in the 1790s.
Celsius
The degree Celsius (°C) is the SI's everyday temperature unit. One degree Celsius is exactly the same size as one kelvin, with the zero point shifted so that 0 °C = 273.15 K. Water freezes near 0 °C and boils near 100 °C at standard atmospheric pressure.
Named for Swedish astronomer Anders Celsius, who in 1742 proposed a 100-degree scale between the boiling and freezing points of water. His original scale ran in reverse (0 at boiling, 100 at freezing); it was inverted to the modern direction shortly after his death.
The world's standard everyday temperature scale, used in nearly every country — including throughout India — for weather forecasts, cooking, medicine, science classrooms, and industry.
Devised by Anders Celsius at Uppsala University, Sweden, in 1742; the inverted modern form was in use by 1745, and the name 'degree Celsius' replaced 'degree centigrade' internationally at the 9th CGPM in 1948.
Réaumur to Celsius conversion formula
The exact relationship between degrees réaumur and degrees celsius:
To convert degrees réaumur to degrees celsius, multiply the value in degrees réaumur by 5/4. To reverse, multiply the value in degrees celsius by 4/5.
Both units count upward from absolute zero, so 0 °Ré = 0 °C and the relationship is a pure ratio.
How to use this converter
Type a value into the calculator. The result in degrees celsius updates as you type. Tap a quick value, copy the result with one click, or use the swap arrow to jump straight to the Celsius to Réaumur converter for the reverse direction.
Step-by-step: convert degrees réaumur to degrees celsius
- Write down the temperature in degrees réaumur (°Ré).
- Multiply the value in degrees réaumur by 5/4.
- The result is the same temperature expressed in degrees celsius (°C).
- To reverse, multiply the value in degrees celsius by 4/5 — or open the Celsius to Réaumur converter.
Worked examples
Example 1 — Convert 29.6 °Ré to °C (human body temperature):
29.6 × 5/4 = 37 °C
Example 2 — Convert 80 °Ré to °C (the boiling point of water):
80 × 5/4 = 100 °C
Réaumur to Celsius conversion table
Physically meaningful reference temperatures, from absolute zero to the surface of the Sun, converted from degrees réaumur to degrees celsius:
| Réaumur [°Ré] | Celsius [°C] | Reference point |
|---|---|---|
| -218.52 | -273.15 | Absolute zero |
| -32 | -40 | Where Celsius and Fahrenheit coincide (−40°) |
| -14.2222222222 | -17.7777777778 | Zero Fahrenheit (0 °F) |
| 0 | 0 | Water freezes (0 °C / 32 °F) |
| 0.008 | 0.01 | Triple point of water |
| 8 | 10 | Cool day (10 °C / 50 °F) |
| 16 | 20 | Room temperature (20 °C / 68 °F) |
| 20 | 25 | Standard laboratory temperature (25 °C) |
| 24 | 30 | Hot day (30 °C / 86 °F) |
| 29.6 | 37 | Human body temperature (37 °C / 98.6 °F) |
| 32 | 40 | Heat-wave day (40 °C / 104 °F) |
| 40 | 50 | Hot tap water (50 °C / 122 °F) |
| 80 | 100 | Water boils (100 °C / 212 °F) |
| 144 | 180 | Moderate baking oven (180 °C / 356 °F) |
| 4403.88 | 5504.85 | Surface of the Sun (≈5,505 °C) |
Frequently asked questions
How many degrees celsius is 1 degree réaumur?
How do I convert degrees réaumur to degrees celsius?
How do I convert degrees celsius back to degrees réaumur?
How many degrees celsius is 80 degrees réaumur?
Can a temperature be below absolute zero?
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Modern Standard Scales (4 units)
Historical Scales (3 units)
Scientific & Fixed-Point (3 units)
Sources & references
Conversion relationship (1 °Ré = 1.25 °C) verified against the following authoritative sources:
- BIPM — The International System of Units (SI Brochure 9th ed.)
Official BIPM publication defining the seven SI base units (including the meter) and the rules for their use. The global authority on units of measurement.
- NIST — Guide to the SI
US National Institute of Standards and Technology reference covering the SI base and derived units with definitions and usage rules for US technical practice.
- NIST Special Publication 811 — Guide for the Use of the International System of Units
Detailed NIST guide covering exact conversion factors between SI and US customary units along with formatting and rounding conventions.
- BIPM — International Temperature Scale of 1990 (ITS-90)
The internationally agreed practical temperature scale, defining fixed points (including the triple point of water at 273.16 K) and interpolation instruments used by national metrology institutes for thermometer calibration worldwide.
- CODATA Internationally Recommended Values of the Fundamental Physical Constants
Committee on Data of the International Science Council; authoritative source for the masses of fundamental particles (electron, proton, neutron) and the atomic mass constant.