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Rankine (°R) to Kelvin Converter

Enter a value in rankine (°r) to convert it to kelvin, celsius.

Result

294.44 K
21.29 °C

How it is calculated

Rankine and kelvin both start at absolute zero, so converting is a pure scale factor with no offset: K = °R × 5/9. The tool uses 5/9 written as 0.5555555556. It then gives Celsius from the kelvin value with °C = K − 273.15. The input is a temperature in degrees Rankine; both results are rounded to two decimals. For example 0 °R is 0 K and −459.67 °F. The tool does not stop you from entering a negative Rankine value, which is physically impossible because nothing can be colder than absolute zero, so check any negative result before using it. To go back, multiply kelvin by 9/5.

Worked example

An engineering table gives a gas temperature of 530 °R. Kelvin: 530 × 5/9 = 530 × 0.5555555556 = 294.44, shown as 294.44 K. Celsius: 294.4444 − 273.15 = 21.29, shown as 21.29 °C. In Fahrenheit the same temperature is 530 − 459.67 = 70.33 °F, which is a normal room temperature, so the value is plausible for an indoor gas.

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Common mistakes

  • Subtracting 459.67 and calling it Rankine. Subtracting gives Fahrenheit; Rankine is the Fahrenheit value plus 459.67, so 70.33 °F is 530 °R.
  • Multiplying by 9/5 when going to kelvin. To get kelvin from Rankine you multiply by 5/9, a smaller number; 9/5 is for the opposite direction.
  • Adding 273.15 to the Rankine value. That offset belongs to Celsius-to-kelvin and has no role in Rankine-to-kelvin.
  • Entering a negative Rankine number. The scale starts at 0 °R (absolute zero), so a negative input is not a real temperature, even though the tool prints a result for it.

About this calculator

The Rankine scale is an absolute temperature scale — like Kelvin, its zero point is absolute zero — but it uses Fahrenheit-sized degrees instead of Celsius-sized ones. The conversion is simply K = °R × 5/9 (the same 5/9 ratio that relates Fahrenheit degrees to Celsius degrees), so water's freezing point, 491.67°R, converts to 273.15 K.

US aerospace, mechanical, and HVAC engineers working in Fahrenheit-based unit systems still use Rankine in thermodynamic calculations — ideal gas law, combustion, and compressible-flow equations that require an absolute temperature — specifically because it lets them keep every other measurement in familiar Fahrenheit-based units while still satisfying the "temperature must be absolute" requirement those formulas demand.

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