🌡️ °R to K — Rankine to Kelvin Converter

Convert Rankine to Kelvin. Used when converting US engineering data to SI units for scientific calculations.

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Formula K = °R × 5/9

All Rankine conversions

Unit	Name	Value
°C	Celsius	-272.59444
°F	Fahrenheit	-458.67
K	Kelvin	0.55555556

Related Temperature conversions

°C → °F °F → °C °C → K K → °C °F → K

⚡ How to Convert Rankine to Kelvin

Multiply by 5/9 (≈ 0.5556). Formula: K = °R × 5/9. Example: 540°R × 5/9 = 300 K. Reverse: °R = K × 9/5.

Worked Examples

Example 1 — Converting US legacy table to SI calculation

671.67°R × 5/9 = 373.15 K

An older American steam table lists a boiler temperature as 671.67°R. An engineer applying the Clausius-Clapeyron equation (which requires Kelvin) converts to 373.15 K — the boiling point of water — to calculate vapour pressure correctly.

Example 2 — Aerospace — converting NASA spec to SI

2880°R × 5/9 = 1600 K

A NASA legacy document specifies turbine inlet temperature as 2880°R. A European aerospace supplier must verify this against their own specifications in Kelvin — it converts to 1600 K, within the operating range of modern single-crystal turbine blades.

Example 3 — Cryogenics — US liquid hydrogen spec to Kelvin

36.5°R × 5/9 = 20.28 K

A US aerospace component datasheet specifies liquid hydrogen storage at 36.5°R. Scientists applying quantum thermodynamic models (which require Kelvin) convert to 20.28 K — the boiling point of LH₂ used in rocket propellant calculations.

Example 4 — Process engineering — converting Rankine output

900°R × 5/9 = 500 K

A legacy US process simulation outputs reactor temperature as 900°R. The engineer converts to 500 K to use in a modern kinetics model that requires SI units, ensuring the activation energy calculation is correctly performed.

Rankine to Kelvin — Reference Table

Rankine (°R)	Kelvin (K)	Real-world context
0°R	0 K	Absolute zero — both scales start here
138.87°R	77.15 K	Liquid nitrogen boiling point
491.67°R	273.15 K	Water freezing point
536.67°R	298.15 K	Standard thermodynamic reference (25°C)
558.27°R	310.15 K	Human body temperature
671.67°R	373.15 K	Water boiling point
1800°R	1000 K	Industrial furnace range
10400.4°R	5778 K	Surface of the Sun

Mental Math Tricks for °R ↔ K

Divide by 1.8 — that's it

°R ÷ 1.8 = K. Both start at zero. 540°R ÷ 1.8 = 300 K. No offset constant needed.

Reverse: multiply by 1.8

K × 1.8 = °R. 300 K × 1.8 = 540°R.

Anchor: 540°R = 300 K

A convenient round-number anchor. Scale proportionally — every 18°R = 10 K.

No offset — unlike all other conversions

Fahrenheit↔Celsius needs ±32. Celsius↔Kelvin needs ±273.15. But Rankine↔Kelvin needs only a multiplication — the simplest temperature conversion between different scales.

Who Uses This Conversion?

Real professions and situations that need °R to K conversion

🔬

Scientists Receiving US Engineering Data

When US engineering partners or contractors provide temperatures in Rankine, scientists applying thermodynamic equations (which universally require Kelvin) must convert before any calculation.

🏭

International Engineers Using US Software

Engineers outside the US working with American process simulation software (Aspen, HYSYS with Rankine settings) extract Rankine outputs and convert to Kelvin for their SI-based calculations and reports.

🎓

International Students Using US Textbooks

Engineering students from Europe, Asia or Australia studying with American thermodynamics textbooks encounter Rankine in examples. Converting to Kelvin validates answers against their SI-based lecture notes.

✈️

European Aerospace Suppliers to US Primes

Airbus, Rolls-Royce, Safran and other European suppliers receiving Boeing or Lockheed thermal specs in Rankine convert to Kelvin for their own design and analysis tools, all of which use SI units.

📐

SI Standards Harmonisation Engineers

Engineers converting ASME/API standards (which may use Rankine) to ISO/EN equivalents (Kelvin) for international product certification must perform this conversion for every temperature reference in the documents.

💡

Energy Research Scientists

Researchers analysing US energy efficiency data — often published in BTU-per-hour and Rankine — convert to SI units (watts and Kelvin) for publication in international journals and comparison with global datasets.

All Rankine Conversions

Frequently Asked Questions

Multiply by 5/9: K = °R × 5/9. Example: 540°R × 5/9 = 300 K.

0°R equals 0 K — both scales start at absolute zero. No offset is needed for this conversion.

491.67°R equals 273.15 K — the freezing point of water.

671.67°R equals 373.15 K — the boiling point of water.

Because both Rankine and Kelvin start at absolute zero. There is no additive offset — just a multiplicative factor of 5/9. This makes it the simplest of all cross-scale temperature conversions.

536.67°R equals 298.15 K — the standard thermodynamic reference temperature (25°C).

1°R equals 5/9 K ≈ 0.5556 K. The Rankine degree is smaller than the Kelvin because Fahrenheit degrees are smaller than Celsius degrees.

About Rankine and Kelvin

Rankine (°R)

The Rankine scale (symbol: °R) was proposed by William John Macquorn Rankine in 1859 as an absolute temperature scale using Fahrenheit degree intervals. Starting at absolute zero (0°R = 0 K), it provides an absolute reference without requiring the −273.15 offset of Celsius-to-Kelvin conversion.

Used primarily in US engineering thermodynamics, Rankine remains in legacy aerospace documentation, chemical engineering software and ASME standards. Rankine was a professor at the University of Glasgow and one of the founders of thermodynamics, also known for developing the Rankine cycle — the theoretical basis of steam power plants.

Kelvin (K)

The Kelvin (symbol: K) is the SI base unit of thermodynamic temperature, universally used in science and international engineering. Starting at absolute zero, it shares degree intervals with Celsius (0°C = 273.15 K). No degree symbol is used — write 300 K, not 300°K.

Defined since 2019 by the Boltzmann constant (k = 1.380649×10⁻²³ J/K), the Kelvin is the primary absolute temperature scale worldwide. All major thermodynamic equations (ideal gas law, Stefan-Boltzmann, Arrhenius) require temperature in Kelvin. The scale was named after Lord Kelvin by decision of the CGPM in 1954.

Common use: Rankine-to-Kelvin conversion is needed when bringing US engineering data into SI-based scientific calculations. The absence of any additive offset (just multiply by 5/9) makes this the most mathematically elegant of all temperature scale conversions.