The Rankine scale

°R = °F + 459.67

Rankine is an absolute temperature scale that uses Fahrenheit-sized degrees. It starts at absolute zero (0 °R = −459.67 °F), so it never goes negative. Water freezes at 491.67 °R and boils at 671.67 °R at sea level. Rankine is to Fahrenheit what Kelvin is to Celsius.

Rankine

°R

Fahrenheit

°F

Celsius

°C

Kelvin

Decimals

Rankine, Kelvin, Celsius and Fahrenheit landmarks

Landmark	°R	°F	K	°C
Absolute zero	0	−459.67	0	−273.15
Liquid nitrogen boils	139.25	−320.42	77.36	−195.79
Dry ice sublimes	350.37	−109.3	194.65	−78.5
−40 crossover	419.67	−40	233.15	−40
Water freezes	491.67	32	273.15	0
Standard sea-level air (ISA, 59 °F)	518.67	59	288.15	15
Room (68 °F)	527.67	68	293.15	20
Body (98.6 °F)	558.27	98.6	310.15	37
Water boils (sea level)	671.67	212	373.15	100
Moderate oven (350 °F)	809.67	350	449.82	176.67

Two absolute scales, two degree sizes

An absolute scale puts its zero where molecular motion is at its minimum, so doubling the number really does double the thermal energy measure. That is what gas laws like PV = nRT need. Kelvin does this with Celsius-sized steps; Rankine does it with Fahrenheit-sized steps, which are 5/9 as big. So the same temperature always reads 1.8 times higher in °R than in K: 300 K = 540 °R.

William Rankine proposed the scale in 1859, a few years after William Thomson (Lord Kelvin) proposed his. Today Rankine survives mainly in US engineering that works in customary units, such as HVAC, power-plant and aerospace thermodynamics, where formulas use BTU and pounds alongside °R.

All Rankine formulas

°R = °F + 459.67 and °F = °R − 459.67
°R = (°C + 273.15) × 9/5 and °C = (°R − 491.67) × 5/9
°R = K × 9/5 and K = °R × 5/9

Rankine chart

°R	°F	°C	K
0	−459.67	−273.15	0
50	−409.67	−245.37	27.78
100	−359.67	−217.59	55.56
150	−309.67	−189.82	83.33
200	−259.67	−162.04	111.11
250	−209.67	−134.26	138.89
300	−159.67	−106.48	166.67
350	−109.67	−78.71	194.44
400	−59.67	−50.93	222.22
450	−9.67	−23.15	250
500	40.33	4.63	277.78
550	90.33	32.41	305.56
600	140.33	60.18	333.33
650	190.33	87.96	361.11
700	240.33	115.74	388.89
750	290.33	143.52	416.67
800	340.33	171.29	444.44
850	390.33	199.07	472.22
900	440.33	226.85	500
950	490.33	254.63	527.78
1000	540.33	282.41	555.56
1050	590.33	310.18	583.33
1100	640.33	337.96	611.11
1150	690.33	365.74	638.89
1200	740.33	393.52	666.67

Rankine converters

Questions

What is the Rankine temperature scale?

An absolute temperature scale with Fahrenheit-sized degrees. 0 °R is absolute zero, and °R = °F + 459.67.

What does Rankine mean?

The scale is named after William John Macquorn Rankine, the Scottish engineer and physicist who proposed it in 1859. The unit is the degree Rankine, symbol °R (sometimes °Ra to avoid confusion with Réaumur).

Are Rankine and Kelvin the same?

Both start at absolute zero, but their degrees differ in size: one kelvin equals 1.8 °R. So °R = K × 9/5 and K = °R × 5/9.

How do I convert Rankine to Fahrenheit?

Subtract 459.67: °F = °R − 459.67. For example 530 °R is 70.33 °F.

Why do engineers and NASA use Rankine?

Gas laws and thermodynamic equations need an absolute temperature. Engineers working in US customary units (pounds, BTU, feet) use Rankine so the numbers stay consistent with Fahrenheit-sized degrees; NASA Glenn Research Center's Beginner's Guide to Aeronautics, for instance, gives standard-atmosphere temperatures in °R alongside °F.

Can Rankine be negative?

No. Like Kelvin, Rankine starts at absolute zero, so every physical temperature is zero or positive.