Fidamen

Convert Celsius to Reaumur - Temperature Converter

This tool converts a single temperature value from degrees Celsius (°C) to degrees Réaumur (°Ré). The Réaumur scale is a linear temperature scale historically used in parts of Europe; its defined ratio to Celsius makes conversions straightforward and exact with basic arithmetic.

Use this converter for quick calculations, lab note conversions, recipe adjustments, and documentation where the Réaumur scale is referenced. For metrology or legal requirements, ensure your measured temperatures are obtained from calibrated instruments traceable to recognized standards.

Updated Nov 23, 2025QA PASS — golden 25 / edge 120Run golden-edge-2026-01-23

Governance

Record 7c22619a1784 • Reviewed by Fidamen Standards Committee

Interactive Converter

Convert between celsius and reaumur with precision rounding.

Quick reference table

CelsiusReaumur
1 °C0.8 °Ré
5 °C4 °Ré
10 °C8 °Ré
25 °C20 °Ré
50 °C40 °Ré
100 °C80 °Ré

Methodology

The Réaumur scale is defined so that the freezing point of water is 0°Ré and the boiling point of water at standard pressure is 80°Ré. Celsius is defined with freezing 0°C and boiling 100°C. Because both scales are linear and share the same zero for the freezing point of water, the conversion is a simple linear scaling.

For measurement-grade work, conversions assume temperatures have been measured according to recognized protocols (for example ITS-90 and instrument calibration). Converting a recorded temperature is a mathematical operation that does not change measurement uncertainty; always propagate instrument uncertainty when reporting converted values.

Key takeaways

Convert °C to °Ré by multiplying by 4/5 (0.8). Reverse by multiplying °Ré by 5/4 (1.25). The arithmetic is exact; reported precision should reflect measurement uncertainty and calibration status.

Worked examples

Example 1: 100 °C → 100 × 4/5 = 80 °Ré

Example 2: -10 °C → -10 × 4/5 = -8 °Ré

F.A.Q.

Is the conversion exact?

Mathematically the conversion factor (4/5 or 0.8) between Celsius and Réaumur is exact because both are linear scales with fixed ratios. However, reported converted values inherit the measurement uncertainty of the original temperature reading. For traceable measurements, follow NIST/ISO-recommended calibration and uncertainty reporting procedures.

Do I need to calibrate instruments before converting values?

Calibration is a property of the measuring instrument, not the conversion. If your results must comply with metrology or regulatory requirements, ensure instruments are calibrated and traceable to standards such as ITS-90. Converting calibrated readings preserves the numeric transformation but does not reduce measurement uncertainty.

What rounding or precision should I use?

Choose significant digits consistent with the original measurement uncertainty. For everyday use, two decimal places is usually sufficient. For laboratory or legal reporting, follow your lab's uncertainty and significant-figure policies and document the uncertainty alongside the converted value.

Are there regulatory references I should follow for temperature measurement?

Yes. For metrology and calibration use NIST guidance on temperature and ITS-90. ISO standards cover quantities and units for thermodynamics. Occupational exposure limits and workplace temperature guidance can come from OSHA. Consult the specific standards applicable to your industry when measurements are used for compliance.

Can I convert extremely large or small temperatures with this formula?

The linear conversion works across the numeric range of the scales, but practical limits depend on measurement method and instrument range. For extreme temperatures near instrument limits or requiring thermodynamic temperature definitions, refer to ITS-90 and instrument manufacturer specifications.

Sources & citations

Further resources

Versioning & Change Control

Audit record (versions, QA runs, reviewer sign-off, and evidence).

Record ID: 7c22619a1784

What changed (latest)

v1.0.0 • 2025-11-23 • MINOR

Initial publication and governance baseline.

Why: Published with reviewed formulas, unit definitions, and UX controls.

Public QA status

PASS — golden 25 + edge 120

Last run: 2026-01-23 • Run: golden-edge-2026-01-23

Engine

v1.0.0

Data

Baseline (no external datasets)

Content

v1.0.0

UI

v1.0.0

Governance

Last updated: Nov 23, 2025

Reviewed by: Fidamen Standards Committee (Review board)

Credentials: Internal QA

Risk level: low

Reviewer profile (entity)

Fidamen Standards Committee

Review board

Internal QA

Entity ID: https://fidamen.com/reviewers/fidamen-standards-committee#person

Semantic versioning

  • MAJOR: Calculation outputs can change for the same inputs (formula, rounding policy, assumptions).
  • MINOR: New features or fields that do not change existing outputs for the same inputs.
  • PATCH: Bug fixes, copy edits, or accessibility changes that do not change intended outputs except for previously incorrect cases.

Review protocol

  • Verify formulas and unit definitions against primary standards or datasets.
  • Run golden-case regression suite and edge-case suite.
  • Record reviewer sign-off with credentials and scope.
  • Document assumptions, limitations, and jurisdiction applicability.

Assumptions & limitations

  • Uses exact unit definitions from the Fidamen conversion library.
  • Internal calculations use double precision; display rounding follows the unit's configured decimal places.
  • Not a substitute for calibrated instruments in regulated contexts.
  • Jurisdiction-specific rules may require official guidance.

Change log

v1.0.0 • 2025-11-23 • MINOR

Initial publication and governance baseline.

Why: Published with reviewed formulas, unit definitions, and UX controls.

Areas: engine, content, ui • Reviewer: Fidamen Standards Committee • Entry ID: 3314141a7756