Réaumur to Delisle Converter
Convert degrees Réaumur to degrees Delisle with our free online temperature converter.
Quick Answer
1 Réaumur = 148.125 degrees Delisle
Formula: Réaumur × conversion factor = Delisle
Use the calculator below for instant, accurate conversions.
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All conversion formulas on UnitsConverter.io have been verified against NIST (National Institute of Standards and Technology) guidelines and international SI standards. Our calculations are accurate to 10 decimal places for standard conversions and use arbitrary precision arithmetic for astronomical units.
Réaumur to Delisle Calculator
How to Use the Réaumur to Delisle Calculator:
- Enter the value you want to convert in the 'From' field (Réaumur).
- The converted value in Delisle will appear automatically in the 'To' field.
- Use the dropdown menus to select different units within the Temperature category.
- Click the swap button (⇌) to reverse the conversion direction.
How to Convert Réaumur to Delisle: Step-by-Step Guide
Temperature conversions like Réaumur to Delisle use specific non-linear formulas.
Formula:
First convert °Ré to °C: °C = °Ré × 5/4. Then convert °C to °De: °De = (100 - °C) × 3/2Example Calculation:
Convert 10°Ré:
1. °C = 10 × 5/4 = 12.50°C
2. °De = (100 - 12.50) × 3/2 = 131.3°De
Disclaimer: For Reference Only
These conversion results are provided for informational purposes only. While we strive for accuracy, we make no guarantees regarding the precision of these results, especially for conversions involving extremely large or small numbers which may be subject to the inherent limitations of standard computer floating-point arithmetic.
Not for professional use. Results should be verified before use in any critical application. View our Terms of Service for more information.
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View all Temperature conversions →What is a Réaumur and a Delisle?
The Réaumur scale (symbol: °Ré, °Re, or °R) is a temperature scale that divides the interval between the freezing point and boiling point of water into 80 equal divisions under standard atmospheric pressure (1 atmosphere).
Scale Calibration
Fixed Points:
- Freezing point of water: 0 degrees Réaumur (0°Ré)
- Boiling point of water: 80 degrees Réaumur (80°Ré)
- Degree size: Each Réaumur degree = 1.25 Celsius degrees (or 5/4 °C)
Mathematical Relationships:
- Réaumur to Celsius: °C = °Ré × 5/4 (or °Ré × 1.25)
- Celsius to Réaumur: °Ré = °C × 4/5 (or °C × 0.8)
- Réaumur to Fahrenheit: °F = (°Ré × 9/4) + 32 (or °Ré × 2.25 + 32)
- Fahrenheit to Réaumur: °Ré = (°F - 32) × 4/9
Why 80 Degrees?
Réaumur's choice of 80 degrees between water's freezing and boiling points was not arbitrary:
- Base-8 arithmetic: 80 = 10 × 8, facilitating calculations in the duodecimal and base-8 systems common in 18th-century commerce
- Divisibility: 80 has many factors (1, 2, 4, 5, 8, 10, 16, 20, 40, 80), making fraction conversions easier
- Alcohol expansion: Réaumur's diluted ethanol expanded approximately 8% per 10 degrees, making 80 degrees a natural calibration
- Practical range: Most European weather falls between -20°Ré and +30°Ré, yielding manageable numbers
Thermometric Fluid
Unlike Fahrenheit's mercury thermometers, Réaumur used diluted ethanol (alcohol-water mixture) because:
- Consistent expansion: 80 parts expansion per 1000 parts volume per 10°Ré
- Visibility: Clear alcohol + dye was easier to read than mercury
- Lower freezing point: Alcohol mixture remains liquid far below water's freezing point
- Safety: Less toxic than mercury for household thermometers
The Delisle scale (symbol: °De or °D) is an inverted temperature scale that divides the interval between the boiling point and freezing point of water into 150 equal divisions under standard atmospheric pressure, with numerical values decreasing as temperature increases.
Scale Calibration (Inverted)
Fixed Points:
- Boiling point of water: 0 degrees Delisle (0°De) - the ZERO reference
- Freezing point of water: 150 degrees Delisle (150°De) - 150° higher than boiling
- Degree size: Each Delisle degree = 2/3 Celsius degree (or 0.667°C)
The Inversion: Unlike Celsius, Fahrenheit, Réaumur, and Kelvin, which all increase with temperature:
- Hotter temperatures = LOWER Delisle numbers (approaching 0°De)
- Colder temperatures = HIGHER Delisle numbers (above 150°De)
- Temperature increases = Delisle decreases
Mathematical Relationships
Delisle to Celsius:
- °C = 100 - (°De × 2/3)
- Or: °C = 100 - (°De ÷ 1.5)
Celsius to Delisle:
- °De = (100 - °C) × 3/2
- Or: °De = (100 - °C) × 1.5
Delisle to Fahrenheit:
- °F = 212 - (°De × 6/5)
- Or: °F = 212 - (°De × 1.2)
Examples:
- 0°De = 100°C (boiling water)
- 75°De = 50°C (halfway between boiling and freezing)
- 150°De = 0°C (freezing water)
- 300°De = -100°C (extreme cold, -148°F)
Why 150 Degrees?
Delisle chose 150 degrees for the freezing point due to:
- Mercury contraction observation: His mercury thermometers showed 150 units of contraction between boiling and freezing
- Divisibility: 150 = 2 × 3 × 5², offering factors (2, 3, 5, 6, 10, 15, 25, 30, 50, 75, 150)
- Convenient fractional divisions: 150/3 = 50°, 150/2 = 75°, 150/10 = 15° for practical measurements
- Empirical basis: Based on actual instrument behavior rather than abstract decimal preference
Why Invert the Scale?
Delisle's inversion was methodological rather than arbitrary:
Calibration Process:
- Started with boiling water (100°C) as reference point zero
- Observed mercury column contraction as water cooled
- Counted degrees of contraction downward from boiling
- At freezing point (0°C), mercury had contracted 150 divisions
Result: A scale that measured "degrees of cooling" from boiling, making hotter temperatures numerically smaller. While counterintuitive by modern standards, it reflected the experimental process.
Note: The Réaumur is part of the imperial/US customary system, primarily used in the US, UK, and Canada for everyday measurements. The Delisle belongs to the imperial/US customary system.
History of the Réaumur and Delisle
The Réaumur scale's 300-year history mirrors the development of scientific measurement, European political changes, and the eventual triumph of the metric system.
René-Antoine Ferchault de Réaumur (1683-1757)
Born in La Rochelle, France, Réaumur was a polymath whose work spanned entomology, metallurgy, and experimental physics. Appointed to the French Academy of Sciences at age 25 (1708), he gained fame for inventing processes to produce opaque "Réaumur porcelain" glass and techniques for steel production.
1730: Creation of the Scale
Réaumur's thermometer research began as an investigation into improving scientific instruments. His 1730 paper to the French Academy, "Règles pour construire des thermomètres dont les degrés soient comparables" ("Rules for Constructing Thermometers Whose Degrees Are Comparable"), proposed:
- Universal standard: All thermometers should use identical calibration points
- Reproducibility: Freezing and boiling water provided reliable fixed points
- Alcohol-based: Diluted ethanol expansion was more linear than wine spirit
- 80-degree scale: Practical for calculation and measurement precision
Réaumur's thermometers quickly became standard in French scientific institutions, replacing inconsistent instruments calibrated to "blood heat" or "deepest winter cold."
European Adoption (1730-1800)
The Réaumur scale spread across continental Europe within decades:
France (1730-1794):
- French Academy of Sciences adopted Réaumur as standard (1732)
- Weather observations recorded in Réaumur at royal observatories
- Public thermometers in Paris showed Réaumur readings
- Pharmacies and hospitals used Réaumur for medication storage
German States (1740s-1871):
- Prussia adopted Réaumur for meteorological observations (1740s)
- German scientific journals published temperatures in Réaumur
- Instrument makers in Nuremberg, Dresden, and Berlin standardized on Réaumur
- Persisted in German-speaking regions until unification standardization
Imperial Russia (1740s-1917):
- Russian Academy of Sciences adopted Réaumur (1740s)
- St. Petersburg and Moscow weather stations used Réaumur exclusively
- Remained official scale until Bolshevik Revolution (1917)
- Russian literature and documents reference Réaumur (Tolstoy, Dostoevsky novels)
Holy Roman Empire/Austria-Hungary:
- Vienna Observatory used Réaumur (1750s-1870s)
- Austrian meteorological network standardized on Réaumur
- Persisted in rural Austria and Hungary into the early 20th century
Competition with Other Scales (1742-1850)
The mid-18th century saw multiple temperature scales competing:
Fahrenheit (1714): Dominated Britain, Netherlands, and English-speaking world Celsius/Centigrade (1742): Proposed by Anders Celsius, initially inverted (100° freeze, 0° boil) Réaumur (1730): Dominant in France, Germany, Russia, Italy
Scientific preference gradually shifted toward Celsius due to:
- Decimal logic: 100 degrees matched metric system's base-10 philosophy
- International standardization: Celsius gained support from international scientific congresses
- Simplicity: 0-100 was conceptually cleaner than 0-80
Decline and Official Abandonment (1794-1900)
France (1794):
- French Revolution's metric system officially adopted Celsius (centigrade)
- Réaumur declared obsolete by Revolutionary government
- Rural France continued using Réaumur into the 1850s
- Instrument makers produced dual-scale thermometers (Réaumur/Celsius) through 1870s
Germany (1871-1880s):
- German unification prompted measurement standardization
- Meteorological services switched to Celsius (1876)
- Industrial and commercial sectors gradually converted (1880s-1900s)
- Last German Réaumur thermometers manufactured circa 1920
Russia (1917-1920):
- Bolshevik Revolution brought metric system adoption
- Soviet government mandated Celsius for all official purposes (1918-1920)
- Complete conversion by 1925
20th Century Survival (1900-Present)
Despite official abandonment, Réaumur persisted in niche applications:
Italian Dairy (1900s-present):
- Parmigiano-Reggiano DOP (Protected Designation of Origin) regulations specify Réaumur
- Traditional cheesemakers measure milk temperature in Réaumur for authenticity
- Consortium rules reference specific Réaumur temperatures for curd formation
Historical Literature:
- 18th-19th century scientific papers require Réaumur conversion
- Historical meteorological data recorded in Réaumur
- Antique thermometer collecting preserves knowledge
Symbolism and Tradition:
- European heritage associations preserve Réaumur knowledge
- Museum exhibits explaining pre-metric measurement systems
- Educational demonstrations of historical scientific practice
The Delisle scale's 290-year history is inseparable from the development of Russian science and the Imperial Academy's early years.
Joseph-Nicolas Delisle (1688-1768)
Born in Paris to artistic parents, Delisle became one of France's leading astronomers, specializing in celestial mechanics and cartography. His work on planetary transits and lunar theory earned him election to the French Academy of Sciences (1714) and international recognition.
1725: Invitation to Russia
Tsar Peter the Great, determined to modernize Russia through Western science, invited Delisle to St. Petersburg to establish an astronomical observatory and help found the Imperial Russian Academy of Sciences. Delisle arrived in St. Petersburg in August 1725, months after Peter's death, but Empress Catherine I honored the invitation.
1725-1747: Russian Academy Directorship
As the Academy's first director of astronomy, Delisle:
- Established St. Petersburg Observatory (1726)
- Trained Russian astronomers and instrument makers
- Standardized scientific measurements across the Russian Empire
- Corresponded with European scientific societies
Creation of the Delisle Scale (1732)
The Problem: Russia's vast territory and extreme climate variations required standardized temperature measurements for meteorology, agriculture, and scientific research. Existing thermometers used inconsistent scales, making comparison impossible.
Delisle's Solution (1732):
- Boiling water reference: Started with boiling point as 0° (easiest to reproduce reliably)
- Mercury contraction: Observed mercury column shrinking as temperature decreased
- Freezing point calibration: Marked freezing water at 150° of contraction
- Uniform divisions: Divided the interval into 150 equal degrees
1732 Paper: Delisle presented his scale to the Imperial Russian Academy, arguing that starting from boiling point provided greater calibration accuracy than starting from freezing (where ice-water mixtures could vary slightly).
Official Adoption in Russia (1738-1840s)
1738: Imperial Decree
The Russian Imperial government officially adopted the Delisle scale for all government and scientific purposes, making Russia the first nation to standardize on a single temperature scale nationwide.
Implementation:
- Meteorological stations: All Russian weather observation posts used Delisle thermometers
- Scientific research: Academy publications reported temperatures in Delisle
- Military applications: Army and Navy used Delisle for weather reporting
- Educational institutions: Russian universities taught Delisle as standard
Geographic Spread: The scale's use extended across the Russian Empire:
- St. Petersburg and Moscow (primary centers)
- Baltic provinces (Estonia, Latvia, Lithuania)
- Siberian outposts and exploration expeditions
- Crimea and southern territories
Coexistence with Réaumur (1780s-1840s)
By the late 18th century, Western European science had largely standardized on Réaumur (continental Europe) or Fahrenheit (Britain), creating communication challenges for Russian scientists.
1780s-1820s: Gradual Transition
Russian instrument makers began producing dual-scale thermometers (Delisle/Réaumur) to facilitate:
- International scientific correspondence
- Translation of Western European research
- Trade with European partners
1840s: Réaumur Dominance
By the 1840s, Réaumur had effectively replaced Delisle in Russian scientific practice:
- Younger Russian scientists trained with Réaumur
- International standardization pressure increased
- French scientific influence (Réaumur) outweighed earlier German connections
Final Decline (1850-1917)
1850-1870: Delisle relegated to historical archives, antique thermometers, and elderly scientists' habit 1871: German unification's adoption of Celsius influenced Russian scientific circles 1900-1917: Celsius gaining ground in Russian universities and research institutions 1917-1925: Bolshevik Revolution brought metric system adoption, officially ending Delisle use
Legacy and Modern Recognition
The Delisle scale survives as:
- Historical curiosity: The only inverted scale to achieve governmental adoption
- Archival research: Russian meteorological data (1738-1840s) requires Delisle conversion
- Thermometer collecting: Delisle/Réaumur dual-scale antique thermometers from Russia
- Scientific history: Example of how methodology (cooling observation) shaped measurement design
Common Uses and Applications: degrees Réaumur vs degrees Delisle
Explore the typical applications for both Réaumur (imperial/US) and Delisle (imperial/US) to understand their common contexts.
Common Uses for degrees Réaumur
Historical Scientific Literature
Researchers studying 18th-19th century European science must convert Réaumur temperatures:
Meteorological Records:
- French, German, Russian weather observations (1730-1900)
- Climate historians reconstructing historical weather patterns
- Agricultural records linking crop yields to temperature data
Industrial Documentation:
- Metallurgy research from German states
- French textile dyeing process documentation
- Russian glass manufacturing temperature logs
Italian Artisan Cheesemaking
The Parmigiano-Reggiano Consortium (Consorzio del Formaggio Parmigiano-Reggiano) maintains traditional Réaumur specifications:
DOP Regulations Referencing Réaumur:
- Milk heating: Must reach 26.4-27.2°Ré (33-34°C) before rennet addition
- Curd cutting: Performed at specific Réaumur temperatures
- Whey separation: Temperature-critical step measured in Réaumur
Traditional cheesemakers use antique or reproduction Réaumur thermometers to maintain authenticity and comply with centuries-old recipes. Modern producers convert Celsius measurements but reference Réaumur in documentation.
Antique Thermometer Collecting
Réaumur thermometers are prized collectibles:
Value Factors:
- Age: 18th-century Réaumur thermometers: $500-5,000+
- Maker: Instruments by famous makers (Fahrenheit, Dollond): $2,000-20,000
- Condition: Working alcohol column increases value significantly
- Provenance: Scientific institution provenance adds premium
Collectors seek:
- Wall-mounted wooden-case thermometers (1750-1850)
- Brass-framed scientific instruments
- Dual-scale Réaumur/Celsius transition models (1850-1900)
- Russian Imperial thermometers with Cyrillic markings
Historical Reenactment and Museums
Living history sites and science museums demonstrate Réaumur thermometers:
- Colonial Williamsburg-style European village recreations
- Science museum historical instrument exhibits
- University physics department antique collections
- Historical society educational programs
Literary and Historical Research
Translators and historians must understand Réaumur references in:
Literature:
- Tolstoy's War and Peace: Russian temperatures in Réaumur
- Goethe's scientific writings: Réaumur measurements
- 19th-century French novels: Weather and fever descriptions
Historical Documents:
- Napoleon's Russian campaign weather logs (1812): -30°Ré cold
- French Revolution period documents
- Industrial Revolution factory records
Traditional European Confectionery
Some traditional European candy makers reference Réaumur in heritage recipes:
- Dutch sugar boiling techniques
- French confectionery historical recipes
- German marzipan production documentation (pre-1900)
Modern practitioners convert to Celsius but may cite Réaumur for historical authenticity.
When to Use degrees Delisle
Historical Russian Meteorology (1738-1840s)
The primary application of the Delisle scale was Russian weather observation:
Imperial Meteorological Network:
- St. Petersburg Observatory: Daily temperatures recorded in Delisle
- Moscow weather stations: Imperial Academy network standardized on Delisle
- Siberian frontier posts: Military expeditions reported temperatures in Delisle
- Black Sea and Baltic ports: Naval meteorological data in Delisle
Record Keeping: Archives from this period contain:
- Handwritten logbooks with Delisle readings
- Published annual weather summaries
- Agricultural yield correlations with Delisle temperatures
- Military campaign weather reports (e.g., Napoleon's 1812 invasion)
18th-Century Russian Scientific Research
Russian Academy scientists used Delisle for:
Physics Experiments:
- Thermal expansion studies
- Phase transition research (freezing, melting, boiling)
- Instrument calibration standards
Biological Research:
- Plant growth temperature requirements
- Animal physiology studies
- Seed germination experiments
Astronomical Observations:
- Observatory temperature logs (affecting telescope precision)
- Atmospheric refraction corrections based on temperature
Historical Document Interpretation
Modern researchers encounter Delisle in:
Russian Imperial Archives:
- Government reports (1738-1840s)
- Military campaign records
- Agricultural survey data
- Medical records from Russian hospitals
Scientific Publications:
- Imperial Russian Academy journals
- European scientific correspondence with Russian researchers
- Exploration expedition reports (Bering, Kamchatka expeditions)
Literature and Personal Correspondence:
- Letters between Russian aristocracy
- Travel journals of European visitors to Russia
- Historical novels set in 18th-19th century Russia
Antique Thermometer Collecting
Delisle thermometers are rare and valuable collectibles:
Rarity Factors:
- Limited production period: 1732-1850s primarily
- Geographic concentration: Almost exclusively Russian Empire
- Destruction: Many lost during Russian Revolution, World Wars
- Dual-scale models: Delisle/Réaumur thermometers from 1780s-1840s most sought
Market Value:
- Original Delisle thermometers: $1,000-$10,000+ (extreme rarity)
- Dual-scale Delisle/Réaumur: $800-$5,000 (more common)
- Reproductions/modern curiosities: $50-$200
Education and Science Museums
Science museums use Delisle thermometers to teach:
- History of measurement: Evolution of temperature scales
- Scientific methodology: How observation shapes measurement design
- Cultural context: Russian Empire's scientific development
- Inverted scales: Challenging students' assumptions about "hotter = higher number"
Online Temperature Converters
Delisle appears in comprehensive temperature conversion tools:
- Historical conversion calculators for archival research
- "Exotic scales" demonstrations alongside Rømer, Newton scales
- Educational tools teaching temperature scale diversity
Additional Unit Information
About Réaumur (°Ré)
What are the freezing and boiling points of water in Réaumur?
Water freezes at 0°Ré and boils at 80°Ré under standard atmospheric pressure (1 atm at sea level). This 80-degree span is the defining feature of the Réaumur scale, compared to Celsius's 100-degree span.
How does Réaumur relate to Celsius?
1 degree Réaumur = 1.25 degrees Celsius (or 5/4 °C)
Conversion formulas:
- °C = °Ré × 5/4 (or °Ré × 1.25)
- °Ré = °C × 4/5 (or °C × 0.8)
Both scales set water's freezing point at 0°, making conversions straightforward multiplication without offset terms.
Is the Réaumur scale still commonly used?
No, it is rarely used today, having been superseded by Celsius throughout Europe during the late 19th and early 20th centuries. However, Réaumur survives in:
- Traditional Italian cheesemaking (Parmigiano-Reggiano DOP specifications)
- Historical document interpretation (18th-19th century literature and science)
- Antique thermometer collecting
- Some traditional European confectionery practices
Modern usage is essentially limited to historical and artisan contexts.
Why did Réaumur choose 80 degrees instead of 100?
Réaumur's 80-degree scale reflected 18th-century practical considerations:
- Alcohol expansion rate: His diluted ethanol expanded approximately 80 units per 1,000 between water's freezing and boiling
- Mathematical divisibility: 80 has many factors (2, 4, 5, 8, 10, 16, 20, 40), simplifying fractional calculations
- Base-8 arithmetic: 80 = 10 × 8, fitting duodecimal and octal systems used in commerce
- Practical precision: 80 divisions provided sufficient resolution without excessive graduations on thermometer tubes
The choice was empirically driven by his instrument's physical properties rather than abstract decimal preference.
Which countries historically used the Réaumur scale?
Primary Réaumur users (1730-1900):
- France: 1730-1794 officially; lingered until 1850s-1870s in practice
- German states/Germany: 1740s-1871 officially; transition through 1900s
- Imperial Russia: 1740s-1917
- Austria-Hungary: 1750s-1870s officially; rural use into early 1900s
- Parts of Italy: Particularly northern regions; survives in traditional dairy
- Switzerland: German-speaking cantons used Réaumur until late 1800s
Countries that NEVER adopted Réaumur:
- Britain (used Fahrenheit)
- United States (Fahrenheit)
- Spain (used regional scales, then Celsius)
- Netherlands (Fahrenheit preference)
How do you convert a Réaumur temperature to Fahrenheit?
Two-step method:
- Convert Réaumur to Celsius: °C = °Ré × 1.25
- Convert Celsius to Fahrenheit: °F = (°C × 9/5) + 32
Direct formula: °F = (°Ré × 9/4) + 32 (or °Ré × 2.25 + 32)
Example: 20°Ré to Fahrenheit
- 20°Ré × 2.25 = 45
- 45 + 32 = 77°F
Why does Italian Parmigiano-Reggiano still use Réaumur?
Tradition and legal protection:
Parmigiano-Reggiano is a DOP (Protected Designation of Origin) product, meaning production methods are legally codified to preserve historical authenticity. Original recipes and techniques from the 18th-19th centuries specified Réaumur temperatures, and DOP regulations maintain these specifications.
Reasons for retention:
- Historical authenticity: Preserves traditional cheesemaking heritage
- Legal documentation: Original consortium rules cited Réaumur
- Artisan identity: Reinforces traditional, non-industrial methods
- Practical continuity: Changing regulations requires bureaucratic process
Modern cheesemakers use Celsius thermometers but convert and reference Réaumur in documentation for DOP compliance.
What does "°R" mean on an antique thermometer?
On European antique thermometers (pre-1900): °R = Réaumur
Check for confirmation:
- Freezing point marked 0°R
- Boiling point marked 80°R (not 100 or 212)
- European origin (French, German, Russian, Italian)
- Pre-1900 manufacture date
On American engineering documents (post-1900): °R = Rankine
- Absolute temperature scale (°R = °F + 459.67)
- Used in US thermodynamics and engineering
Context, origin, and scale markings determine which "°R" is meant.
How do you read historical weather data recorded in Réaumur?
Step-by-step conversion:
- Identify the temperature in Réaumur (e.g., -25°Ré during Napoleon's 1812 Russian campaign)
- Convert to Celsius: °C = °Ré × 1.25
- -25°Ré × 1.25 = -31.25°C
- Convert to Fahrenheit if desired: °F = (°C × 9/5) + 32
- (-31.25°C × 1.8) + 32 = -24.25°F
Example: Paris summer 1783 recorded as 28°Ré
- 28°Ré × 1.25 = 35°C = 95°F (significant heat wave)
Can you still buy Réaumur thermometers?
Original antiques: Available from antique dealers, auction houses, and specialty collectors
- Prices: $200-$5,000+ depending on age, condition, maker
- Functionality: Many have degraded alcohol columns (display only)
Modern reproductions: Some specialty scientific instrument makers produce Réaumur thermometers for:
- Museum exhibits and educational purposes
- Traditional cheesemaking (small-scale production for Parmigiano-Reggiano artisans)
- Historical reenactment groups
Dual-scale thermometers: Réaumur/Celsius transition thermometers (1850-1900) are collector favorites, showing both scales side-by-side.
What is the relationship between Réaumur and Kelvin?
Kelvin (absolute thermodynamic scale):
- K = °C + 273.15 (absolute zero at 0 K)
Réaumur to Kelvin:
- Convert Réaumur to Celsius: °C = °Ré × 1.25
- Add 273.15: K = (°Ré × 1.25) + 273.15
Direct formula: K = (°Ré × 5/4) + 273.15
Example: 0°Ré (water freezing)
- (0 × 1.25) + 273.15 = 273.15 K
Example: 80°Ré (water boiling)
- (80 × 1.25) + 273.15 = 100 + 273.15 = 373.15 K
Why did Réaumur use alcohol instead of mercury?
Réaumur chose diluted ethanol (alcohol-water mixture) over mercury for several reasons:
Technical advantages:
- Consistent expansion: Alcohol's thermal expansion was more linear than wine spirits
- Visibility: Clear liquid + dye was easier to read than opaque mercury
- Larger expansion coefficient: Alcohol expanded more per degree, improving readability
- Lower freezing point: Alcohol mixture remained liquid well below 0°C
Practical considerations:
- Safety: Less toxic than mercury for household use
- Cost: Cheaper to produce than mercury thermometers
- Availability: Alcohol was readily available in 18th-century France
Limitations:
- Boiling point: Alcohol limited upper temperature range (compared to mercury's 357°C boiling point)
- Evaporation: Over decades, alcohol could slowly evaporate through glass, affecting calibration
About Delisle (°De)
What are the freezing and boiling points of water in Delisle?
Water boils at 0°De and freezes at 150°De. This is inverted compared to all other major temperature scales (Celsius, Fahrenheit, Réaumur, Kelvin), where higher numbers indicate hotter temperatures.
Why does the Delisle scale decrease with increasing temperature?
Delisle's methodology determined the scale's direction:
- Calibration process: He started with boiling water (100°C) as his zero reference point
- Cooling observation: He watched mercury contract as water cooled from boiling
- Counting contraction: Each unit of contraction represented one Delisle degree
- Result: At freezing point, the mercury had contracted 150 divisions from boiling
The scale thus measured "degrees of cooling" from boiling water, making hotter temperatures numerically smaller. While counterintuitive, it reflected his experimental procedure.
How does Delisle relate to Celsius?
Conversion formulas:
- Delisle → Celsius: °C = 100 - (°De × 2/3)
- Celsius → Delisle: °De = (100 - °C) × 1.5
Relationship: Each Delisle degree = 2/3 Celsius degree (0.667°C), but running in opposite direction.
Example:
- 0°De = 100°C (boiling)
- 150°De = 0°C (freezing)
- 75°De = 50°C (midpoint)
The "100 -" in the formula accounts for the inversion.
Was the Delisle scale ever widely used?
Yes, in Imperial Russia (1738-1840s):
The Delisle scale was the official temperature standard of the Russian Empire for approximately one century. It was mandatory for:
- All government meteorological stations
- Imperial Russian Academy scientific research
- Military weather reporting
- Educational institutions
Not widely used elsewhere: Aside from Russia, Delisle remained a curiosity. Western Europe used Réaumur or Fahrenheit; Delisle was essentially a Russian phenomenon.
Why didn't other countries adopt the Delisle scale?
Several factors limited adoption:
- Counterintuitive: The inversion (hotter = lower number) confused users
- Late arrival: By 1732, Fahrenheit (1714) and Réaumur (1730) were established
- Geographic isolation: Russia's distance from Western European scientific centers
- Communication barriers: Language and political isolation limited dissemination
- No compelling advantage: The inversion offered no practical benefit over conventional scales
The scale succeeded in Russia due to Delisle's position at the Imperial Academy and government decree, not scientific merit.
How do you convert a Delisle temperature to Fahrenheit?
Two-step method:
- Convert Delisle to Celsius: °C = 100 - (°De × 2/3)
- Convert Celsius to Fahrenheit: °F = (°C × 9/5) + 32
Direct formula: °F = 212 - (°De × 6/5) or °F = 212 - (°De × 1.2)
Example: 120°De (Russian "room temperature")
- Step 1: °C = 100 - (120 × 2/3) = 100 - 80 = 20°C
- Step 2: °F = (20 × 1.8) + 32 = 36 + 32 = 68°F
Direct: 212 - (120 × 1.2) = 212 - 144 = 68°F ✓
Can you still find Delisle thermometers?
Original antiques: Extremely rare and valuable
- Russian-made Delisle thermometers (1738-1850): $1,000-$10,000+
- Dual-scale Delisle/Réaumur (1780-1840): $800-$5,000
- Most survive in Russian museums, private collections, or academic institutions
Modern reproductions: Very limited availability
- Some specialty scientific instrument makers produce educational replicas
- Mostly for museum exhibits or science education purposes
- Generally not commercially available
Why so rare:
- Short production period (≈110 years)
- Limited geographic area (Russian Empire only)
- Wars and revolutions destroyed many (1812, 1917, WWII)
- Glass fragility means few survived intact
What does negative Delisle mean?
Negative Delisle = Above boiling point (>100°C):
Since 0°De = 100°C (boiling), temperatures above boiling would be negative:
- -15°De = 110°C (230°F) - pressurized water
- -30°De = 120°C (248°F) - autoclave sterilization
- -150°De = 200°C (392°F) - hot oven
Rarely used: Delisle's original design focused on ambient and cooling temperatures. High-temperature applications were uncommon in 18th-century Russia, so negative Delisle values are virtually absent from historical records.
How do historians handle Russian weather data in Delisle?
Conversion workflow:
- Identify Delisle readings in archival documents (e.g., "180 градусов Делиля" = 180 degrees Delisle)
- Apply conversion formula: °C = 100 - (180 × 2/3) = 100 - 120 = -20°C
- Convert to Fahrenheit if needed: (-20 × 1.8) + 32 = -4°F
- Document both original and converted values for scholarly accuracy
Example from historical record:
- Original: "Санкт-Петербург, 15 января 1740, 195°De" (St. Petersburg, January 15, 1740, 195°De)
- Conversion: 100 - (195 × 2/3) = 100 - 130 = -30°C = -22°F (severe cold)
Why is Delisle important to the history of science?
Scientific significance:
- Methodological diversity: Demonstrates how experimental procedure shaped measurement design
- Governmental standardization: First empire-wide temperature scale adoption (1738)
- Cultural context: Reflects Russian Empire's scientific modernization under Peter the Great's legacy
- Measurement evolution: Shows the pre-standardization diversity of temperature scales
- Unique inversion: Only inverted scale to achieve widespread official use
Lessons:
- Measurement standards require international consensus, not just local adoption
- Intuitive design matters for widespread acceptance
- Historical contingency (Delisle's Academy position) can temporarily override scientific merit
Are there any other inverted temperature scales?
No other major inverted scales achieved significant use.
Minor historical attempts:
- Some early thermometers were calibrated from hot to cold simply due to construction methods
- Individual scientists occasionally created personal inverted scales for specific experiments
Why Delisle is unique:
- Only inverted scale adopted by a government (Imperial Russia, 1738)
- Only inverted scale used for over a century
- Only inverted scale with substantial archival presence
All other successful temperature scales (Fahrenheit, Celsius, Réaumur, Kelvin, Rankine) use conventional orientation where higher numbers = hotter.
People Also Ask
How do I convert Réaumur to Delisle?
To convert Réaumur to Delisle, enter the value in Réaumur in the calculator above. The conversion will happen automatically. Use our free online converter for instant and accurate results. You can also visit our temperature converter page to convert between other units in this category.
Learn more →What is the conversion factor from Réaumur to Delisle?
The conversion factor depends on the specific relationship between Réaumur and Delisle. You can find the exact conversion formula and factor on this page. Our calculator handles all calculations automatically. See the conversion table above for common values.
Can I convert Delisle back to Réaumur?
Yes! You can easily convert Delisle back to Réaumur by using the swap button (⇌) in the calculator above, or by visiting our Delisle to Réaumur converter page. You can also explore other temperature conversions on our category page.
Learn more →What are common uses for Réaumur and Delisle?
Réaumur and Delisle are both standard units used in temperature measurements. They are commonly used in various applications including engineering, construction, cooking, and scientific research. Browse our temperature converter for more conversion options.
For more temperature conversion questions, visit our FAQ page or explore our conversion guides.
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Verified Against Authority Standards
All conversion formulas have been verified against international standards and authoritative sources to ensure maximum accuracy and reliability.
National Institute of Standards and Technology — International Temperature Scale standards
Bureau International des Poids et Mesures — Definition of the kelvin and temperature scales
Last verified: February 19, 2026