Réaumur to Kelvin Converter
Convert degrees Réaumur to kelvins with our free online temperature converter.
Quick Answer
1 Réaumur = 274.4 kelvins
Formula: Réaumur × conversion factor = Kelvin
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 Kelvin Calculator
How to Use the Réaumur to Kelvin Calculator:
- Enter the value you want to convert in the 'From' field (Réaumur).
- The converted value in Kelvin 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 Kelvin: Step-by-Step Guide
Temperature conversions like Réaumur to Kelvin use specific non-linear formulas.
Formula:
First convert °Ré to °C: °C = °Ré × 5/4. Then convert °C to K: K = °C + 273.15Example Calculation:
Convert 10°Ré:
1. °C = 10 × 5/4 = 12.50°C
2. K = 12.50 + 273.15 = 285.65K
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.
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Need to convert to other temperature units?
View all Temperature conversions →What is a Réaumur and a Kelvin?
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
Kelvin (symbol: K, not °K) is the base unit of thermodynamic temperature in the International System of Units (SI). It is an absolute temperature scale, meaning its zero point (0 K) represents the lowest theoretically possible temperature.
Key characteristics:
- Absolute zero: 0 K = -273.15°C = -459.67°F
- No negative temperatures: (in ordinary matter)
- No degree symbol: Write "273 K" not "273°K"
- Same magnitude as Celsius: 1 K change = 1°C change
Modern Definition (2019): The kelvin is defined by fixing the numerical value of the Boltzmann constant (k) to exactly 1.380649×10⁻²³ joules per kelvin (J/K). This definition links temperature to energy at the atomic level.
Conversion formulas:
- From Celsius: K = °C + 273.15 - Convert C to K
- From Fahrenheit: K = (°F - 32) × 5/9 + 273.15 - Convert F to K
- To Celsius: °C = K - 273.15 - Convert K to C
- To Fahrenheit: °F = (K - 273.15) × 9/5 + 32 - Convert K to F
Important fixed points:
- Absolute zero: 0 K (exactly)
- Water triple point: 273.16 K (0.01°C) - where ice, water, and vapor coexist
- Water freezing: 273.15 K (0°C)
- Water boiling: 373.15 K (100°C)
- Room temperature: ~293 K (20°C)
- Human body: ~310 K (37°C)
Why no degree symbol? Kelvin is an absolute scale starting from a fundamental physical limit (absolute zero), not an arbitrary reference point like Celsius or Fahrenheit. The unit is "kelvin" (lowercase when spelled out), not "degrees Kelvin."
Convert between temperature units: Kelvin converter
Note: The Réaumur is part of the imperial/US customary system, primarily used in the US, UK, and Canada for everyday measurements. The Kelvin belongs to the imperial/US customary system.
History of the Réaumur and Kelvin
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
-
Early Thermodynamics (1840s): Scientists studying heat engines and thermodynamics realized that there must be a lowest possible temperature, where thermal energy reaches its minimum.
-
William Thomson (Lord Kelvin) (1824-1907): British physicist and engineer who proposed the absolute temperature scale in 1848. He later became Baron Kelvin, and the unit was named in his honor.
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Original Proposal (1848): Thomson proposed an absolute thermodynamic temperature scale based on:
- Carnot's theorem on heat engines
- The idea that there exists a temperature at which thermal motion ceases
- Independence from the properties of any particular substance
-
Determination of Absolute Zero: By studying the thermal expansion of gases, scientists extrapolated that gases would theoretically have zero volume at approximately -273°C. This temperature was identified as absolute zero.
-
Original Scale (1848-1954): Thomson's scale was initially called the "absolute scale" or "thermodynamic temperature scale." It used the same degree size as Celsius but started at absolute zero.
-
Triple Point Definition (1954): The 10th CGPM (General Conference on Weights and Measures) officially named the unit "kelvin" (symbol K) and defined it based on the triple point of water:
- Triple point of water = exactly 273.16 K
- This made the kelvin equal in magnitude to the Celsius degree
- Eliminated need for a physical artifact
-
Why 273.15?: This value was chosen to maintain compatibility with the Celsius scale, ensuring that the freezing point of water remained at 0°C (273.15 K) and boiling point at 100°C (373.15 K).
-
Adoption as SI Base Unit (1960): When the International System of Units (SI) was established, the kelvin was designated as one of the seven SI base units for thermodynamic temperature.
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Symbol Change (1967): The symbol was changed from "°K" (degree Kelvin) to just "K" (kelvin) to emphasize its absolute nature and distinguish it from relative scales.
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2019 Redefinition: On May 20, 2019, the kelvin was redefined based on the Boltzmann constant:
- Old definition: Based on triple point of water (273.16 K)
- New definition: Boltzmann constant fixed at exactly 1.380649×10⁻²³ J/K
- Why: Links temperature to fundamental physics (energy per particle)
- Advantage: Can be reproduced in any properly equipped laboratory
- Impact: No change to the scale's size or zero point, only how it's realized
-
Boltzmann Connection: The Boltzmann constant (k) relates the average kinetic energy of particles to temperature: E = (3/2)kT. By fixing k, temperature is now defined through energy.
-
Global Scientific Standard: The kelvin is the only SI base unit for temperature. It's used universally in:
- Physics research
- Chemistry
- Astronomy and astrophysics
- Engineering
- Materials science
- Climate science
-
Practical Usage: While Celsius dominates everyday life in most countries and Fahrenheit in the US, scientists worldwide use kelvin for research, ensuring universal compatibility and precision.
Common Uses and Applications: degrees Réaumur vs kelvins
Explore the typical applications for both Réaumur (imperial/US) and Kelvin (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 kelvins
The kelvin is the standard temperature unit in scientific and technical fields worldwide:
Scientific Research
The universal temperature unit in physics, chemistry, and all scientific disciplines. Essential for ensuring reproducibility and international collaboration.
Scientific applications:
- Thermodynamics and statistical mechanics
- Quantum mechanics and atomic physics
- Chemical kinetics and equilibrium
- Materials science research
- Particle physics experiments
- Cryogenics and low-temperature physics
Why kelvin in science:
- SI base unit (international standard)
- Absolute scale (no negative temperatures)
- Direct relationship to energy (via Boltzmann constant)
- Universal reproducibility
- Required for scientific publications
Convert for scientific work: kelvins to other units
Astronomy and Astrophysics
Standard for measuring stellar temperatures, cosmic phenomena, and space science.
Astronomical uses:
- Star surface temperatures (spectral classification)
- Stellar core temperatures
- Planetary atmosphere temperatures
- Cosmic microwave background (2.7 K)
- Interstellar medium temperature
- Black hole thermodynamics
- Big Bang cosmology
Why kelvin in astronomy:
- Suitable for extreme temperatures (millions of kelvins)
- No confusion with negative values
- International astronomical standard
- Links to blackbody radiation physics
Color Temperature
Standard for describing the color of light sources in photography, cinematography, and lighting design.
Color temperature uses:
- Light bulb specifications (2,700-6,500 K)
- Camera white balance settings
- Video production lighting
- Architectural lighting design
- Display calibration
- Stage and theater lighting
Common values:
- Warm light: 2,700-3,500 K
- Neutral/daylight: 5,000-6,500 K
- Cool light: 6,500-10,000 K
Cryogenics
Essential for ultra-low temperature applications and liquefied gas handling.
Cryogenic applications:
- Liquid nitrogen storage (77 K)
- Liquid helium systems (4 K)
- Superconducting magnets (MRI, particle accelerators)
- Cryopreservation (biological samples)
- Rocket fuel (liquid hydrogen, liquid oxygen)
- Low-temperature physics research
Why kelvin in cryogenics:
- Natural scale for very low temperatures
- Avoids large negative numbers
- Direct relationship to thermal energy
- Industry standard
Materials Science
Critical for studying phase transitions, material properties, and thermal behavior.
Materials applications:
- Melting and boiling points
- Glass transition temperatures
- Superconductor critical temperatures
- Thermal expansion studies
- Heat capacity measurements
- Crystal structure studies
Engineering and Industry
Used in technical specifications where absolute temperature is important.
Engineering uses:
- Thermodynamic calculations (heat engines, refrigeration)
- Gas laws and ideal gas calculations
- Chemical reactor design
- Aerospace engineering (re-entry heat)
- Semiconductor manufacturing
- Industrial process control
Ideal gas law: PV = nRT (where T must be in kelvins)
Climate Science
Standard for scientific climate modeling and atmospheric research.
Climate uses:
- Atmospheric temperature profiles
- Ocean temperature measurements
- Climate model simulations
- Radiative transfer calculations
- Greenhouse gas physics
- Ice core data analysis
Use our kelvin converter for scientific conversions.
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 Kelvin (K)
What is absolute zero?
Absolute zero is 0 K (0 kelvins), which equals -273.15°C or -459.67°F. It's the lowest theoretically possible temperature.
What happens at absolute zero:
- All classical thermal motion of particles stops
- Particles still have quantum mechanical zero-point energy
- Entropy reaches its minimum value (Third Law of Thermodynamics)
- No heat energy can be extracted
Can we reach absolute zero?
- No: Third Law of Thermodynamics says it's impossible to reach in finite steps
- Close approach: Scientists have reached temperatures within billionths of a kelvin
- Asymptotic: Can get arbitrarily close but never exactly 0 K
Why impossible?
- Would require infinite work to remove all thermal energy
- Quantum mechanics prevents complete stillness (zero-point energy)
- Heisenberg uncertainty principle limits precision
Coldest achieved: ~100 picokelvin (0.0000000001 K) in ultra-cold atom experiments
How do you convert Celsius to Kelvin?
Use the formula: K = °C + 273.15
Step-by-step:
- Take the Celsius temperature
- Add 273.15
- Result is in kelvins
Examples:
- 0°C: 0 + 273.15 = 273.15 K (water freezes)
- 20°C: 20 + 273.15 = 293.15 K (room temp)
- 100°C: 100 + 273.15 = 373.15 K (water boils)
- -40°C: -40 + 273.15 = 233.15 K
- -273.15°C: -273.15 + 273.15 = 0 K (absolute zero)
Reverse conversion (Kelvin to Celsius):
- Formula: °C = K - 273.15
- Example: 300 K = 300 - 273.15 = 26.85°C
Why 273.15?
- This offset ensures water freezes at 0°C (273.15 K) and boils at 100°C (373.15 K)
- Maintains same degree size as Celsius
Use our Celsius to Kelvin converter for instant conversions.
Why doesn't Kelvin use the degree symbol?
Kelvin doesn't use the degree symbol (°) because it's an absolute scale, not a relative one.
The reasoning:
- Absolute scale: Starts at absolute zero (a fundamental physical limit), not an arbitrary reference point
- Not "degrees": The term "degree" implies divisions on a scale between arbitrary points
- Official designation: Write "300 K" or "300 kelvins", never "300°K"
Comparison:
- Celsius: 0°C is arbitrary (water freezing), uses degree symbol
- Fahrenheit: 0°F is arbitrary (brine freezing), uses degree symbol
- Kelvin: 0 K is absolute zero (fundamental), no degree symbol
Historical note:
- Originally written as "°K" (degrees Kelvin)
- Changed to just "K" (kelvin) in 1967
- Emphasizes its absolute nature
Other absolute scale:
- Rankine (°R) - absolute Fahrenheit scale, does use degree symbol (less common)
What is the relationship between Kelvin and Celsius?
Kelvin and Celsius have the same degree size, but different zero points.
Key relationships:
- Conversion: K = °C + 273.15
- Same magnitude: 1 K change = 1°C change
- Different zeros: 0 K = -273.15°C
Temperature difference:
- A change of 5°C = a change of 5 K
- If temp increases from 20°C to 25°C, that's a 5°C (or 5 K) increase
- 293.15 K to 298.15 K = same increase
Fixed points:
- Water freezes: 0°C = 273.15 K
- Water boils: 100°C = 373.15 K
- Difference: 100°C = 100 K
Why same size:
- Kelvin was defined to maintain compatibility with Celsius
- Makes conversion simple (just add/subtract 273.15)
- Scientists can use either for temperature differences
Convert between them: K to C | C to K
How do you convert Fahrenheit to Kelvin?
Formula: K = (°F - 32) × 5/9 + 273.15
Step-by-step:
- Subtract 32 from Fahrenheit
- Multiply by 5/9 (or 0.5556)
- Add 273.15
Examples:
- 32°F: (32 - 32) × 5/9 + 273.15 = 273.15 K (water freezes)
- 68°F: (68 - 32) × 5/9 + 273.15 = 293.15 K (room temp)
- 212°F: (212 - 32) × 5/9 + 273.15 = 373.15 K (water boils)
- -40°F: (-40 - 32) × 5/9 + 273.15 = 233.15 K
Reverse conversion (Kelvin to Fahrenheit):
- Formula: °F = (K - 273.15) × 9/5 + 32
- Example: 300 K = (300 - 273.15) × 9/5 + 32 = 80.33°F
Alternative method:
- Convert °F to °C first: °C = (°F - 32) × 5/9
- Then convert °C to K: K = °C + 273.15
Use our Fahrenheit to Kelvin converter for accurate conversions.
What is room temperature in Kelvin?
Room temperature is approximately 293-295 K, which equals 20-22°C (68-72°F).
Standard definitions:
- Scientific standard: 293.15 K (20°C, 68°F)
- Comfortable range: 293-295 K (20-22°C, 68-72°F)
- IUPAC standard: 298.15 K (25°C, 77°F) for chemistry
Common room temps:
- Cool room: 291 K (18°C, 64°F)
- Comfortable: 293 K (20°C, 68°F)
- Warm room: 296 K (23°C, 73°F)
Context matters:
- Laboratories: Often use 293.15 K or 298.15 K as standard
- Home comfort: 293-295 K typical
- Chemical reactions: Often specified at 298 K
Human body comparison:
- Room temp: 293 K
- Body temp: 310 K (37°C)
- Difference: 17 K (or 17°C)
What is color temperature measured in?
Color temperature is measured in kelvins (K).
What it means: Color temperature describes the color appearance of light by comparing it to the color of light emitted by a theoretical "blackbody" heated to that temperature.
Common color temperatures:
- 1,800-2,000 K: Candle flame (warm orange)
- 2,700 K: Incandescent bulb (warm yellow)
- 3,000 K: Halogen bulb (warm white)
- 5,000 K: Daylight (neutral white)
- 5,500-6,000 K: Electronic flash (bright white)
- 6,500 K: Overcast daylight (cool white)
- 10,000+ K: Clear blue sky (very cool blue)
Photography use:
- Cameras adjust white balance based on color temperature
- Tungsten setting: ~3,200 K
- Daylight setting: ~5,600 K
Not actual temperature:
- Light bulb at 2,700 K color temp isn't actually 2,700 K hot
- Refers to color match with blackbody at that temperature
- LED bulbs cool to touch but have high color temperature
Can temperature be negative in Kelvin?
In ordinary circumstances, no. Temperatures in kelvin cannot be negative because 0 K is absolute zero, the lowest possible temperature.
For ordinary matter:
- 0 K is the theoretical minimum
- All physical temperatures are ≥ 0 K
- Negative kelvin would be "colder than absolute zero" - impossible
Exotic exception (negative absolute temperature):
- In special quantum systems, "negative temperature" exists in thermodynamic sense
- NOT colder than absolute zero - actually infinitely hot!
- Occurs in population-inverted systems (lasers, certain spin systems)
- Highly technical and non-intuitive concept
If you calculate negative K:
- You made an error in your conversion
- Check your formula (especially converting from Fahrenheit)
Bottom line: For all practical purposes and everyday physics, temperatures in kelvin are always positive (≥ 0 K).
How is Kelvin different from Celsius?
Kelvin and Celsius differ in their zero point, but have the same degree size.
Key differences:
| Feature | Kelvin | Celsius | |---------|--------|---------| | Zero point | Absolute zero (-273.15°C) | Water freezing (0°C) | | Freezing point | 273.15 K | 0°C | | Boiling point | 373.15 K | 100°C | | Degree symbol | No (just K) | Yes (°C) | | Scale type | Absolute | Relative | | Negative values | No (≥0 K) | Yes (below 0°C) | | Primary use | Science | Everyday (most countries) |
Conversion:
- K = °C + 273.15
- °C = K - 273.15
Same magnitude:
- 1 K change = 1°C change
- Temperature difference of 10°C = 10 K
When to use which:
- Kelvin: Scientific research, absolute calculations, thermodynamics
- Celsius: Daily life, weather, cooking (in metric countries)
Convert between them: K to C | C to K
What temperature is the Sun in Kelvin?
The Sun's surface (photosphere) temperature is approximately 5,778 K (5,505°C or 9,941°F).
Sun's temperature zones:
- Core: ~15,000,000 K (15 million K) - where fusion occurs
- Radiative zone: 7,000,000 K to 2,000,000 K
- Convective zone: 2,000,000 K to 5,800 K
- Photosphere (visible surface): 5,778 K - what we see
- Chromosphere: 4,000-25,000 K
- Corona (outer atmosphere): 1,000,000-3,000,000 K (paradoxically hotter than surface!)
Why kelvin for the Sun:
- Astronomical standard
- Suitable for extreme temperatures
- Links to blackbody radiation and stellar classification
Other stars:
- Red dwarfs: 2,500-4,000 K (cooler, redder)
- Sun-like stars: 5,000-6,000 K (yellow)
- Blue giants: 10,000-50,000 K (hotter, bluer)
Spectral classification: Based on surface temperature in kelvins
People Also Ask
How do I convert Réaumur to Kelvin?
To convert Réaumur to Kelvin, 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 Kelvin?
The conversion factor depends on the specific relationship between Réaumur and Kelvin. 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 Kelvin back to Réaumur?
Yes! You can easily convert Kelvin back to Réaumur by using the swap button (⇌) in the calculator above, or by visiting our Kelvin to Réaumur converter page. You can also explore other temperature conversions on our category page.
Learn more →What are common uses for Réaumur and Kelvin?
Réaumur and Kelvin 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