This free temperature converter changes Celsius (°C) into Rankine (°Ra) and back, instantly and in your browser. Rankine is an absolute temperature scale — its zero is absolute zero — but it uses Fahrenheit-sized degrees, which makes it useful in some US engineering and thermodynamics calculations.
How it works
Rankine combines two ideas: the absolute zero reference of Kelvin and the degree size of Fahrenheit. Converting from Celsius means scaling by 1.8 (to switch to Fahrenheit-sized degrees) and adding the offset that shifts the zero to absolute zero:
°Ra = °C × 1.8 + 491.67
This is equivalent to (°C + 273.15) × 9/5. To reverse it, subtract 491.67 and divide by 1.8: °C = (°Ra − 491.67) ÷ 1.8. The additive offset makes the conversion non-proportional, unlike length or mass.
Reference table
| Celsius (°C) | Rankine (°Ra) | Context |
|---|---|---|
| −273.15 °C | 0 °Ra | Absolute zero |
| −17.78 °C | 459.67 °Ra | 0 °F (Fahrenheit zero) |
| 0 °C | 491.67 °Ra | Water freezing point |
| 20 °C | 527.67 °Ra | Room temperature |
| 37 °C | 558.27 °Ra | Human body temperature |
| 100 °C | 671.67 °Ra | Water boiling point |
Where Rankine appears in practice
Rankine is rarely encountered outside a specific corner of US engineering. The most common contexts are:
- Thermodynamics textbooks using US customary units. Many American engineering curricula teach steam tables, psychrometrics, and combustion analysis in Rankine because Fahrenheit is the familiar degree size for students but an absolute scale is needed for equations like PV = nRT.
- Aviation and aerospace engineering in the US, where older standards and tooling still reference Rankine in equations for airspeed, specific impulse, and enthalpy.
- Rankine cycle analysis. The Rankine cycle — the thermodynamic model for steam power plants — is named after William Rankine, the Scottish engineer who developed it, but the cycle itself is equally described in Kelvin. The scale just shares the name.
Outside the US and these niche domains, Kelvin is universally preferred for absolute-temperature work. If you are converting for a non-US audience or modern SI context, Celsius → Kelvin is the standard path; Celsius → Rankine is for US legacy calculations.
One practical check: if you ever see a temperature above 450 in a US thermodynamics context and the surrounding values look like Fahrenheit-sized degrees, the author is almost certainly using Rankine. Room temperature (around 20 °C, 68 °F) corresponds to roughly 528 °Ra, which is a useful sanity-check value to remember. Absolute zero at 0 °Ra and the ice point at 491.67 °Ra bracket the low end of the scale in the same way that 0 K and 273.15 K do for Kelvin.
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