This temperature converter instantly converts values between modern and legacy scales including Celsius, Kelvin, Fahrenheit, Rankine and the rare Reaumur, Delisle, Newton and Rømer. The tool runs in any browser on desktop or mobile and updates results interactively as you type, making it handy for lab notes, engineering checks and everyday conversions.
Table of Contents
What this converter does
- Convert temperatures among eight scales with a single reliable pivot point, Kelvin, for maximum numerical accuracy.
- Handle negative numbers and enforce the physical limit of absolute zero for each scale to prevent impossible inputs.
- Provide immediate output as formatted text for quick reading and as an exact numeric value for copying into calculations.
- Offer compact unit symbols such as °C and K beneath gauges and full scale names inside the result line for clarity.
- Work without installation and remain responsive on slow devices and mobile networks.
Supported scales
| Code | Name | Symbol | Typical use |
|---|---|---|---|
| C | Celsius | °C | Everyday measurements, science and engineering |
| K | Kelvin | K | SI base for thermodynamic calculations |
| F | Fahrenheit | °F | Domestic use in the United States |
| R | Rankine | °R | Absolute scale used in some engineering contexts |
| Re | Réaumur | °Re | Historic European scale, rare but appears in old references |
| De | Delisle | °De | Historic scale found in archival tables |
| N | Newton | °N | Early scientific scale, used historically |
| Ro | Rømer | °Ro | Antique scale, useful for interpreting older documents |
All conversions pass through Kelvin to minimize round off when chaining transforms. First translate the input scale into Kelvin then convert Kelvin into the target scale. Described in words, convert Fahrenheit by subtracting 32, multiply the result by five ninths, then add 273.15 to obtain Kelvin. Convert Réaumur by multiplying the value by 1.25 then adding 273.15 to obtain Kelvin.
How to convert into Kelvin
- Celsius to Kelvin: add 273.15 to the Celsius value.
- Kelvin to Kelvin: use the value as is.
- Fahrenheit to Kelvin: subtract 32 from the Fahrenheit value, multiply by five ninths, then add 273.15.
- Rankine to Kelvin: multiply the Rankine value by five ninths.
- Réaumur to Kelvin: multiply Réaumur by 1.25 then add 273.15.
- Delisle to Kelvin: subtract two thirds of the Delisle value from 100 then add 273.15.
- Newton to Kelvin: multiply Newton by 100 over 33 then add 273.15.
- Rømer to Kelvin: subtract 7.5 from the Rømer value, multiply by 40 over 21 then add 273.15.
How to get other scales from Kelvin
- Kelvin to Celsius: subtract 273.15.
- Kelvin to Fahrenheit: subtract 273.15, multiply by nine fifths, then add 32.
- Kelvin to Rankine: multiply Kelvin by nine fifths.
- Kelvin to Réaumur: subtract 273.15 then multiply by 0.8.
- Kelvin to Delisle: subtract 273.15, multiply by 1.5 then subtract from 100.
- Kelvin to Newton: subtract 273.15 then multiply by 0.33.
- Kelvin to Rømer: subtract 273.15, multiply by 21 over 40 then add 7.5.
Precise formula examples
| Convert | Formula | Worked example |
|---|---|---|
| Celsius to Fahrenheit | F equals C times nine fifths plus thirty two | 10 °C gives 50 °F |
| Fahrenheit to Celsius | C equals F minus thirty two times five ninths | 86 °F gives 30 °C |
| Celsius to Kelvin | K equals C plus 273.15 | 15 °C gives 288.15 K |
| Kelvin to Celsius | C equals K minus 273.15 | 310 K gives 36.85 °C |
Practical notes and behavior
- Absolute zero is enforced so the converter blocks or corrects entries below the physical minimum for the chosen scale.
- Displayed numbers use readable rounding for the interface while the copyable output remains as precise floating point where required.
- Negative temperatures are valid and the slider and input accept decimal values for fine tuning.
- Historic scales are included to simplify work with archival material and older scientific literature.
- When doing thermodynamic calculations use Kelvin as the working unit to avoid unit mistakes in formulas that require absolute temperature.
Conversion examples
- 7 °C converts to 280.15 K and to 44.6 °F
- 125 °C converts to 398.15 K and to 257 °F
- −60 °C converts to 213.15 K and to −76 °F, note the match point between Celsius and Fahrenheit does not occur here
- 24 °C converts to 297.15 K and to 75.2 °F
- 320 K converts to 46.85 °C and to 116.33 °F
FAQ
Can I use fractional values? Yes, type decimals in the input. The slider defaults to integer steps but you can enter precise numbers by hand.
Why route conversions through Kelvin? Using Kelvin avoids cumulative rounding when chaining transforms and matches thermodynamic formulas that require absolute temperature.
How is invalid input handled? The tool checks against absolute zero for the selected input scale and prevents conversions that would produce non physical results.
Recommendations
- For physics and engineering work use Kelvin in formulas that depend on absolute temperature.
- For documentation use Celsius or Fahrenheit depending on your audience, and always include the unit label for clarity.
- When sharing data between systems send the numeric value plus the canonical unit to avoid ambiguity.
This temperature converter is suitable for fast daily conversions and for preliminary scientific checks. Use the precise numeric output for calculations and the rounded display for human readable reports.
Further reading
- Fundamentals of Thermodynamics by Richard E. Sonntag and Claus Borgnakke
- Thermodynamics An Engineering Approach by Yunus A. Cengel and Michael A. Boles
- Heat and Thermodynamics by Mark W. Zemansky and Richard H. Dittman
David Parry — Senior Engineering Analyst
Specializing in electronics and physics-based simulations with 20+ years of engineering experience. David ensures the mathematical and physical accuracy of the tools at ProCalcLab.
