Rankine to Kelvin Converter — Convert °R to K (Exact: K = °R × 5/9)
Accurate Rankine (°R) to Kelvin (K) converter using the exact identity K = °R × 5/9. Ideal for thermodynamics, aerospace, power cycles, cryogenics, process engineering, and education.
Exact identity: K = °R × 5/9. Explore more in our free temperature metric calculators hub.
About Rankine to Kelvin Conversion
Rankine (°R) and Kelvin (K) are both absolute temperature scales anchored at absolute zero. Rankine uses Fahrenheit-sized degree steps, while Kelvin uses Celsius-sized steps. If your legacy datasets, textbooks, or U.S.-centric standards express absolute temperatures in °R, converting them to K aligns your work with SI practice, makes equations and models portable, and avoids confusion when collaborating with international teams.
Rankine to Kelvin Formula
Exact relationship
Because both scales share the same zero, only the degree size changes:
K = °R × 5/9Examples:
491.67 °R × 5/9 = 273.15 K
540.00 °R × 5/9 = 300.00 KReverse calculation (K → °R)
Invert the transform to return to Rankine:
°R = K × 9/5Related Temperature Converters
What is Rankine?
Rankine is an absolute scale using Fahrenheit increments. It appears in U.S.-centric thermodynamics literature, power-plant calculations, and some aerospace documentation. Because it’s absolute, there are no negative absolute temperatures in °R—making it suitable for energy equations, just like Kelvin.
What is Kelvin?
Kelvin is the SI base unit for thermodynamic temperature. Temperature differences in K map directly to energy-based relationships, which is why engineering models, sensor calibrations, and physical chemistry equations standardize on Kelvin for calculations and simulations.
Step-by-Step: Converting °R to K
- Record the temperature in °R.
- Multiply by 5/9 to rescale degree size.
- Report the result in K, rounding only for display.
Walkthrough examples:
Freezing point (absolute): 491.67 °R → 273.15 K
Room temperature: 527.67 °R → 293.15 K
Body temperature: 558.27 °R → 310.15 KCommon Conversions
Everyday checks for thermodynamics & power cycles
| °R | K |
|---|---|
| 0.00 | 0.00 |
| 138.60 | 77.00 |
| 491.67 | 273.15 |
| 527.67 | 293.15 |
| 536.67 | 298.15 |
| 671.67 | 373.15 |
Precision, Rounding & Significant Figures
Operational rounding
Align the number of decimals with your sensors and audience. Executive dashboards often use whole numbers; commissioning logs might use one decimal; lab notebooks and model validation can justify two or more decimals. Keep raw values unrounded and round only when you present a final number to users.
Consistent documentation
Standardize variable and column names (e.g., temp_R, temp_K). Convert once at the pipeline edge; avoid round-trip conversions that can introduce drift. Add a short note such as: “Conversion uses K = °R × 5/9 (absolute scales with identical zero).”
Where This Converter Is Used
- 🛩️ Aerospace & propulsion: Converting legacy °R documentation to K for model inputs and cross-team reviews.
- ⚙️ Power & energy: Brayton/Rankine cycle analysis and heat-rate reporting standardized in SI.
- 🧪 Thermodynamics labs: Absolute temperatures for calorimetry, gas laws, and heat capacity work.
- ❄️ Cryogenics & materials: Very low absolute temperatures where precise deltas in K matter for properties and safety limits.
- 🎓 Education: Demonstrations of absolute scales and conversions while teaching SI best practices.
Quick Reference Table
| K | °R |
|---|---|
| 0.00 | 0.00 |
| 77.00 | 138.60 |
| 273.15 | 491.67 |
| 293.15 | 527.67 |
| 298.15 | 536.67 |
| 373.15 | 671.67 |
Frequently Asked Questions
What is the exact formula to convert Rankine to Kelvin?
Use K = °R × 5/9. Rankine and Kelvin share the same absolute zero, but their degree increments follow Fahrenheit and Celsius, respectively. The 5/9 factor maps Fahrenheit-sized degrees to Celsius-sized degrees without any offset, so the transform is linear and exact across the entire range.
Why convert from Rankine to Kelvin?
Kelvin is the SI base unit used in thermodynamics, heat transfer, and material science because differences in K map directly to energy changes. Converting legacy or U.S.-centric Rankine values to K brings your data in line with international standards, makes equations consistent, and keeps models and documentation interoperable.
Is 491.67 °R really equal to 273.15 K?
Yes. Because °R = K × 9/5, the freezing point of water at 273.15 K corresponds to 273.15 × 9/5 = 491.67 °R. These anchor points are great for quick instrument checks or spreadsheet validation when auditing conversions.
How do I convert Kelvin back to Rankine?
Use the inverse: °R = K × 9/5. In software and analytics pipelines, convert once at the boundary, store the higher-precision raw values, and round only for display to avoid accumulation of rounding error.
Does Rankine use a degree symbol?
Yes—Rankine is written with a degree symbol (°R). Kelvin never uses the degree symbol; correct notation is 300 K, not 300 °K. Keeping notation clean avoids confusion in specs, plots, and code comments.
What precision should I show when reporting Kelvin?
Let the instrument and audience guide you. Dashboards and quick briefs often use whole K or one decimal. Lab notebooks and calibration logs may keep two or more decimals. Keep raw values unrounded in storage and round only at the presentation layer.
Can I convert °R to °F or °C first and then to K?
You can, but it adds steps and intermediate rounding. The direct transform K = °R × 5/9 is exact and simpler. If you need °C or °F for presentation, generate them in parallel from the Kelvin result in your final view.
Is the conversion valid for very low cryogenic temperatures?
Yes. Both Kelvin and Rankine are absolute scales with the same zero, so the linear identity holds across cryogenic ranges. Just ensure your rounding matches sensor resolution—small changes can be meaningful in cryo work.
Where is Rankine still used?
In U.S.-centric thermodynamics texts, some aerospace documentation, power-plant cycle analysis, and legacy standards that grew around Fahrenheit-sized increments. Converting those values to Kelvin aligns them with modern SI practice.
Do temperature differences behave the same in K and °R?
Temperature differences are proportional: ΔK = Δ°R × 5/9. Because both scales are absolute, deltas map directly without offsets—one reason engineers prefer these for energy-based equations.
Tips for Working with °R & K
- Store high-precision Kelvin as your canonical value; generate °R, °C, and °F at presentation time.
- Make unit labels explicit in tables, plots, and API responses—mixing absolute and relative scales causes costly errors.
- When collaborating with international teams, present Kelvin side-by-side with °C for readability while keeping models in K.
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