Contents
How the converter works
Enter degrees Réaumur to multiply the value by 5/4 and get Celsius. The converter starts with 16 °Ré = 20 °C, accepts negative and decimal values, and also calculates backwards from the Celsius field.
Why the factor is 5/4
The two scales place the reference freezing point at zero, but the interval to the boiling point is divided into 80 Réaumur degrees and 100 Celsius degrees. One degree Réaumur therefore spans 1.25 Celsius degrees.
For the reverse direction, use .
Three useful checks
16 °Ré equals 20 °C. Multiply 16 by 1.25. This is the initial value shown by the calculator.
80 °Ré equals 100 °C. The upper reference interval makes a quick check for a missing or inverted factor.
-8 °Ré equals -10 °C. The same multiplication applies below zero, and the minus sign remains.
Use either field
Type the known temperature on the left and read the result on the right. Editing the right field performs the reverse conversion. The middle button swaps the values and scales.
The selectors also offer Fahrenheit and kelvin. A decimal point or comma is accepted, and the display keeps at most two decimal places.
Conversion does not add measurement accuracy
The factor is exact, but a rounded or approximate source remains approximate after conversion. Keep more digits during a technical calculation and round only the final value.
Reference freezing and boiling points describe conventional conditions; real phase-change temperatures can vary with pressure. The calculator converts scale readings and does not model those physical conditions.
Réaumur to Celsius questions
These answers cover the factor, reverse conversion, signs, and displayed precision.
What is the Réaumur-to-Celsius formula?
Multiply degrees Réaumur by 5/4, or 1.25: °C = °Ré × 5/4.
What is 20 °Ré in Celsius?
20 °Ré equals 25 °C.
How do I convert Celsius back to Réaumur?
Multiply Celsius by 4/5, or 0.8.
Can I convert a negative Réaumur value?
Yes. Use the same factor and keep the minus sign; -4 °Ré equals -5 °C.
Why can the result have decimals?
One Réaumur degree equals 1.25 Celsius degrees, so whole inputs do not always produce whole results.
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