Simple ratio
Multiplies Celsius by 0.8 with no offset.
Enter a Celsius temperature to calculate degrees Réaumur, Fahrenheit, and Kelvin, with a clear formula and common freezing and boiling reference values.
Degrees Réaumur (°Ré) = degrees Celsius × 4 ÷ 5. Reverse: °C = °Ré × 5 ÷ 4.
Multiplies Celsius by 0.8 with no offset.
Explains where the Réaumur scale may appear.
Shows Fahrenheit and Kelvin alongside the result.
Multiply the Celsius value by 4/5, or 0.8, to obtain degrees Réaumur. Both scales place the freezing point of water at zero under their traditional reference definitions, but the boiling interval is divided differently: 100 Celsius degrees correspond to 80 Réaumur degrees.
The Réaumur scale is historical and is uncommon in modern general measurement, but it appears in older scientific, industrial, culinary, and archival materials. When interpreting a historical value, verify the source notation and context because old instruments and conventions may not match modern measurement accuracy.
The converter displays modern mathematical equivalents. Reference freezing and boiling points depend on pressure, sample composition, and measurement conditions, so they should not be treated as universal calibration values outside their stated conditions.
| Input | What it means | Planning note |
|---|---|---|
| -40 °C | -32 °Ré | Below the shared zero reference. |
| 0 °C | 0 °Ré | Traditional water freezing reference. |
| 25 °C | 20 °Ré | Room-temperature example. |
| 100 °C | 80 °Ré | Traditional boiling interval reference near standard pressure. |
Interpret temperatures in archival scientific or technical text.
Convert older culinary and production temperature notations.
Compare how temperature scales divide reference intervals.
100 °C equals 80 °Ré.
Multiply Celsius by 4/5, or 0.8.
It is uncommon in modern general measurement but can appear in historical or specialized references.
Their traditional water-freezing reference is 0 on both scales, so no offset is needed.
Last reviewed: August 13, 2026. Formulas use exact defined scale relationships; displayed results are rounded for readability.
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