Rankine to Kelvin Converter
Quick Conversion: K = R × 5/9
Rankine to Kelvin Converter
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How to Convert Rankine to Kelvin
The formula is:
K = R × 5/9
Temperature conversion chart
| To Fahrenheit | To Celsius | To Kelvin | |
| From Fahrenheit (F) | F | (F - 32) × 5/9 | (F - 32) × 5/9 + 273.15 |
| From Celsius (C or o) | (C × 9/5) + 32 | C | C + 273.15 |
| From Kelvin (K) | (K - 273.15) × 9/5 + 32 | K - 273.15 | K |
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About the Rankine
Facts & Uses
- Absolute temperature scale using Fahrenheit-sized degrees: 0 °R = absolute zero, 491.67 °R = water freezing, 671.67 °R = water boiling.
- Used in US engineering disciplines — particularly thermodynamics, propulsion, HVAC, and aerospace — where absolute temperature is needed but Fahrenheit-sized increments are preferred.
- Conversion is simple: °R = °F + 459.67 exactly. The relationship to Kelvin is K = °R × 5/9.
- Found in steam tables, combustion analysis, and NIST reference data for the United States engineering community.
Curiosities
- Proposed by William John Macquorn Rankine (1820-1872), Scottish engineer and physicist, in 1859 — eleven years after Kelvin proposed his absolute scale.
- Rankine is the only widely-used absolute scale based on the Fahrenheit increment; its existence persists because US engineering standards predate metrication.
- One Rankine degree equals one Fahrenheit degree in size (5/9 of a Kelvin), so temperature differences in Rankine = temperature differences in Fahrenheit.
- Most modern textbooks and ISO standards have moved to Kelvin even in the US, but Rankine still appears in mechanical engineering reference tables and FAA aviation publications.
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About the Kelvin
Facts & Uses
- SI base unit of thermodynamic temperature. Since 2019, defined by fixing the Boltzmann constant at exactly 1.380649 × 10⁻²³ J/K (26th CGPM).
- Universal in physics, chemistry, astronomy (star surface temperatures), and cryogenics — anywhere the absolute scale matters.
- Anchor points: 0 K = absolute zero (theoretical lowest temperature, no thermal motion), 273.15 K = water freezing, 373.15 K = water boiling at 1 atm.
- Real-world references: ~3 K cosmic microwave background, 77 K liquid nitrogen, 4.2 K liquid helium, 5778 K Sun's surface.
Curiosities
- Named after William Thomson, Lord Kelvin (1824-1907), who proposed an absolute thermodynamic scale in 1848.
- The Kelvin is the only base SI unit not written with a degree symbol — write "300 K", never "300 °K". This was standardized at the 13th CGPM (1967).
- Until 2019, the Kelvin was defined by the triple point of water (273.16 K exactly). The 2019 redefinition switched to a fixed Boltzmann constant for stability.
- The lowest temperature ever achieved in a lab is about 38 picokelvins (3.8 × 10⁻¹¹ K), at the Hannover Institute in 2021 — quantum gas experiments.
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Looking for the reverse? Convert Kelvin to Rankine
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All unit conversions on CoolConversion use conversion factors defined or documented by internationally recognised standards bodies (such as ISO and NIST), including both SI and non-SI units.
Related in other categories:
- Joules to kWh — Kelvin used in thermodynamic energy calculations
Conversion factors verified against NIST, BIPM, ITS-90 (International Temperature Scale)
Defined by the absolute thermodynamic scale (Kelvin).
Last reviewed: March 2026
