Convert Reaumur to Celsius - Temperature Converter

This tool converts temperatures from the Réaumur scale (°Ré) to the Celsius scale (°C) using the exact linear relationship between the two scales. It is intended for quick conversions, documentation, and educational use.

The conversion implemented here is a pure mathematical transformation and does not account for measurement uncertainty from instruments or environmental factors. For metrology, calibration, or regulated reporting, follow recognized standards and laboratory procedures cited below.

Updated Nov 28, 2025QA PASS — golden 25 / edge 120Run golden-edge-2026-01-23

Governance

Record 3ed50a5c23a8 • Reviewed by Fidamen Standards Committee

Interactive Converter

Convert between reaumur and celsius with precision rounding.

Reaumur (°Ré)Celsius (°C)

Quick reference table

Reaumur	Celsius
1 °Ré	1.25 °C
5 °Ré	6.25 °C
10 °Ré	12.5 °C
25 °Ré	31.25 °C
50 °Ré	62.5 °C
100 °Ré	125 °C

Methodology

Réaumur and Celsius are both interval temperature scales tied to fixed reference points (ice point and boiling point of water). Because the Réaumur scale sets water boiling at 80°Ré and Celsius at 100°C, the scales are related linearly.

This converter applies the exact scale factor derived from the fixed points. No empirical calibration or sensor corrections are applied by this tool. For traceable measurements, calibrate instruments per ISO/IEC 17025 and document measurement uncertainty as recommended by NIST and international metrology guidance.

Key takeaways

The conversion is exact and linear: multiply Réaumur by 1.25 to get Celsius.

Use this converter for quick arithmetic transformations. For any scientific, calibration, or compliance use, ensure instrument traceability and uncertainty reporting following metrology standards.

Worked examples

0 °Ré → 0 °C (freezing point of water)

80 °Ré → 100 °C (boiling point of water at standard pressure)

12 °Ré → 15 °C (12 × 1.25 = 15)

F.A.Q.

What is the Réaumur scale?

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 pressure. It is now rarely used but still appears in historical documents and some regional applications.

Why multiply by 1.25?

Because the Réaumur scale defines the boiling point of water as 80 units while Celsius defines it as 100 units; 100/80 = 1.25, so °C = °Ré × 1.25.

Is this conversion exact or approximate?

The numerical conversion between scales (°C = °Ré × 1.25) is exact as a mathematical relationship between the defined scales. Reported measurement values may carry instrument uncertainty that this converter does not estimate.

How should I handle measurement uncertainty and calibration?

For measurements used in research, manufacturing, or regulatory contexts, perform instrument calibration and uncertainty analysis. Follow ISO/IEC 17025 for laboratory competence and NIST guidance for temperature measurement and ITS-90 for temperature scale realization.

Are there limits where this conversion does not apply?

The linear conversion applies across the numeric range of both scales as defined. However, for extreme thermodynamic conditions where realization of the scale differs (very low or very high temperatures), consult metrology references and instrument specifications for validity and uncertainty.

Sources & citations

NIST — Temperature and Thermometry (overview and ITS-90 resources) — https://www.nist.gov/pml/weights-and-measures/temperature
ISO — ISO/IEC 17025: General requirements for the competence of testing and calibration laboratories — https://www.iso.org/standard/66912.html
IEEE Standards Overview (sensor and instrumentation standards) — https://standards.ieee.org
OSHA — General requirements for equipment calibration and maintenance guidance — https://www.osha.gov
BIPM — International Bureau of Weights and Measures (metrology and units) — https://www.bipm.org
ISO 80000-5:2019 — Thermodynamics — https://www.iso.org/standard/64976.html
NIST SP 330 — The International System of Units (SI) — https://www.nist.gov/pml/special-publication-330
BIPM SI Brochure (9th edition, 2019) — https://www.bipm.org/en/publications/si-brochure

Further resources

Related tools

External guidance

Versioning & Change Control

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

Record ID: 3ed50a5c23a8

What changed (latest)

v1.0.0 • 2025-11-28 • 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

Governance

Last updated: Nov 28, 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 • 2025-11-28 • 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: b096e8611287