Rankine to Celsius Converter

Convert °R to °C when reading US engineering data, propellant specs or older thermodynamics tables in metric.

°C = (°R − 491.67) × 5/9

Rankine

Result will appear here...

491.67 or 459.67? The Most Common Mistake

Two offsets appear in Rankine conversions, and mixing them up is easy:

459.67 is the gap between Rankine and Fahrenheit. Subtracting it from a Rankine value gives Fahrenheit, not Celsius.
491.67 is the Rankine value of water's freezing point (0°C). Subtract it, then scale by 5/9, to get Celsius.

If your Celsius answer for room-temperature data comes out around 70, you've probably subtracted 459.67 and stopped there. That's the Fahrenheit value.

Rankine to Celsius Formulas

Direct

°C = (°R − 491.67) × 5/9

Through kelvin

°C = °R × 5/9 − 273.15

Resize to kelvin first (both are absolute scales), then apply the Celsius offset. This is handy if you also need the kelvin value.

Cryogenic Propellants: °R to °C

US rocket-engine and propellant documentation often lists temperatures in Rankine. These are normal boiling points at 1 atm.

Boiling points of cryogenic propellants in Rankine, Celsius and kelvin
Fluid	°R	°C	K
Liquid helium (pressurant)	7.6	-268.93	4.22
Liquid hydrogen (LH₂)	36.5	-252.87	20.28
Liquid nitrogen	139.25	-195.79	77.36
Liquid oxygen (LOX)	162.34	-182.96	90.19
Liquid methane (LCH₄)	201.01	-161.48	111.67

Worked Example: Liquid Oxygen

A propellant spec gives the boiling point of liquid oxygen as 162.34°R. In Celsius:

Step 1: Subtract the freezing point of water in °R

162.34 − 491.67 = −329.33

Step 2: Scale to Celsius-sized degrees

−329.33 × 5/9 = −182.96°C

−182.96°C, which matches the 90.19 K boiling point quoted in SI references.

Rankine to Celsius Table

Rankine temperatures converted to Celsius
°R	°C
0°R	-273.15°C
100°R	-217.59°C
200°R	-162.04°C
300°R	-106.48°C
400°R	-50.93°C
459.67°R	-17.78°C
491.67°R	0°C
527.67°R	20°C
600°R	60.18°C
671.67°R	100°C
1,000°R	282.41°C
1,500°R	560.18°C
2,000°R	837.96°C
3,000°R	1,393.52°C