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Convert Reaumur to Fahrenheit - Temperature Converter

This converter converts a temperature measured on the Réaumur scale (°Ré) to the Fahrenheit scale (°F). The Réaumur scale is a historical temperature scale where 0 °Ré is the freezing point of water and 80 °Ré is the boiling point of water at standard atmospheric pressure.

The mathematical relationship between Réaumur and Fahrenheit is exact and linear, so a numeric input in °Ré maps directly to a single °F value. Practical uncertainty in the result comes from how the input temperature was measured and the calibration status of the measuring instrument.

Updated Nov 28, 2025

Interactive Converter

Convert between reaumur and fahrenheit with precision rounding.

Quick reference table

ReaumurFahrenheit
1 °Ré34.25 °F
5 °Ré43.25 °F
10 °Ré54.5 °F
25 °Ré88.25 °F
50 °Ré144.5 °F
100 °Ré257 °F

Methodology

The conversion uses a fixed linear transformation between scales derived from the definitions of Réaumur, Celsius, and Fahrenheit. The formula is algebraically exact: Fahrenheit equals Réaumur multiplied by 9/4, then plus 32.

While the arithmetic conversion itself is exact, for measurements obtained from thermometers or sensors follow metrology best practices: use instruments calibrated to recognized standards, and account for measurement uncertainty. Relevant standards and guidance include the International Temperature Scale (ITS-90), NIST calibration guidance, and laboratory accreditation under ISO/IEC 17025.

Worked examples

Example 1: 20 °Ré → °F = (20 × 9/4) + 32 = (20 × 2.25) + 32 = 45 + 32 = 77 °F.

Example 2: −5 °Ré → °F = (−5 × 9/4) + 32 = (−5 × 2.25) + 32 = −11.25 + 32 = 20.75 °F.

Key takeaways

Use °F = (°Ré × 9/4) + 32 to convert Réaumur to Fahrenheit. The arithmetic is exact; consider instrument calibration and measurement uncertainty when interpreting converted values.

For high-stakes or regulated measurements, rely on calibrated instrumentation with traceability to ITS-90 and laboratories accredited to ISO/IEC 17025. Consult NIST, ISO, IEEE, and OSHA guidance where relevant.

Expert Q&A

Is the conversion exact or approximate?

The mathematical conversion between Réaumur and Fahrenheit is exact because it is a linear scale transformation: °F = °Ré × 9/4 + 32. Any approximation in a reported result comes from numeric rounding or from uncertainty in the measured input temperature.

How many decimal places should I keep?

Choose precision based on application and measurement uncertainty. For everyday use, 1–2 decimal places are typically sufficient. For laboratory or engineering work, match the number of significant digits to the sensor accuracy and calibration certificate uncertainty.

Why do you mention calibration and standards?

Temperature readings depend on instruments. To ensure traceability and meaningful uncertainty estimates, instruments should be calibrated by labs accredited to ISO/IEC 17025 and aligned with reference standards such as ITS-90. Conversion alone does not remove measurement error from the original reading.

Can I convert negative Réaumur values?

Yes. The formula applies to all real numbers. Negative Réaumur values convert normally using the same linear formula.

Does this tool account for measurement uncertainty or sensor drift?

No. This tool performs a pure mathematical conversion. To account for uncertainty or drift, apply your instrument's calibration uncertainty from its certificate or consult an accredited calibration laboratory.

Sources & citations