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Convert between Rankine and Fahrenheit, Celsius, or Kelvin instantly. Essential for engineering thermodynamics, aerospace calculations, and absolute temperature work in Fahrenheit-based systems.
0 °R
Absolute Zero (-459.67 °F)
491.67 °R
Freezing Point of Water
671.67 °R
Boiling Point of Water
Formulas: °F = °R - 459.67 | °C = (°R - 491.67) x 5/9 | K = °R x 5/9
| Rankine (°R) | Fahrenheit (°F) | Celsius (°C) | Kelvin (K) | Significance |
|---|---|---|---|---|
| 0 °R | -459.67 °F | -273.15 °C | 0 K | Absolute zero |
| 459.67 °R | 0 °F | -17.78 °C | 255.37 K | 0 °F reference |
| 491.67 °R | 32 °F | 0 °C | 273.15 K | Freezing point of water |
| 509.67 °R | 50 °F | 10 °C | 283.15 K | Cool day |
| 527.67 °R | 68 °F | 20 °C | 293.15 K | Room temperature |
| 536.67 °R | 77 °F | 25 °C | 298.15 K | Standard conditions (STP) |
| 558.27 °R | 98.6 °F | 37 °C | 310.15 K | Human body temperature |
| 671.67 °R | 212 °F | 100 °C | 373.15 K | Boiling point of water |
| 900 °R | 440.33 °F | 226.85 °C | 500 K | High-temp engineering |
| 1800 °R | 1340.33 °F | 726.85 °C | 1000 K | Metallurgical range |
The Rankine scale (°R) is an absolute thermodynamic temperature scale proposed in 1859 by William John Macquorn Rankine (1820–1872), a Scottish mechanical engineer and physicist at the University of Glasgow. Rankine was one of the founding figures of the science of thermodynamics, alongside Rudolf Clausius, William Thomson (Lord Kelvin), and James Clerk Maxwell. His contributions extend beyond the temperature scale to the famous Rankine cycle, which describes the idealized thermodynamic process in steam turbines and power plants around the world.
Like the Kelvin scale, Rankine is an absolute temperature scale, meaning its zero point corresponds to absolute zero — the theoretical lowest possible temperature where all molecular motion ceases. However, while Kelvin uses Celsius-sized degree increments, Rankine uses Fahrenheit-sized degree increments. This means the Rankine scale is to Fahrenheit what Kelvin is to Celsius. One degree Rankine equals exactly one degree Fahrenheit in size, and one Kelvin equals exactly 1.8 degrees Rankine.
At absolute zero: 0 °R = 0 K = -459.67 °F = -273.15 °C. At the freezing point of water: 491.67 °R = 273.15 K = 32 °F = 0 °C. At the boiling point of water: 671.67 °R = 373.15 K = 212 °F = 100 °C.
The Rankine scale remains in active use in certain branches of U.S. engineering, especially in aerospace, mechanical, and chemical engineering, where Fahrenheit is the standard practical temperature unit. Thermodynamic equations requiring absolute temperature (such as the ideal gas law, entropy calculations, and heat transfer coefficients) work correctly in Rankine when other quantities are expressed in imperial/US customary units.
Three formulas cover all Rankine conversions. Each reflects the relationship between absolute zero offsets and degree sizes across the temperature scales.
Formula: °F = °R - 459.67
Example: Convert 558.27 °R (human body temperature) to Fahrenheit.
The offset 459.67 is the Rankine equivalent of Fahrenheit's zero point above absolute zero.
Formula: °C = (°R - 491.67) × 5/9
Example: Convert 671.67 °R (boiling point of water) to Celsius.
491.67 is the Rankine value at 0 °C. The 5/9 factor converts Fahrenheit-sized degrees to Celsius-sized degrees.
Formula: K = °R × 5/9
Example: Convert 900 °R to Kelvin.
Since both scales start at absolute zero, no offset is needed — only the degree-size ratio of 5/9.
| Description | °R | °F | °C |
|---|---|---|---|
| Absolute zero | 0 | -459.67 | -273.15 |
| Liquid nitrogen boils | 139.33 | -320.33 | -195.79 |
| Dry ice sublimates | 351.07 | -108.60 | -78.11 |
| Freezing point of water | 491.67 | 32 | 0 |
| Comfortable room | 527.67 | 68 | 20 |
| Human body | 558.27 | 98.6 | 37 |
| Boiling point of water | 671.67 | 212 | 100 |
| Oven baking (350 °F) | 809.67 | 350 | 176.67 |
| Lead melts | 1080.07 | 620.4 | 327.5 |
| Iron melts | 3240.27 | 2780.6 | 1538.0 |
| Application | °R | K |
|---|---|---|
| Cryogenic hydrogen fuel | 36.27 | 20.15 |
| LNG storage | 200.07 | 111.15 |
| Standard temperature (STP) | 491.67 | 273.15 |
| Steam turbine inlet (typical) | 1959.67 | 1088.71 |
| Gas turbine combustion | 2759.67 | 1533.15 |
| Rocket nozzle throat | 5859.67 | 3255.37 |
| Surface of the Sun | 10,340 | 5,744 |
Thermodynamic equations like the ideal gas law (PV = nRT), Carnot efficiency, and entropy calculations require absolute temperature. In U.S. engineering practice where pressures are in psi and energy in BTU, Rankine is the natural absolute temperature unit that keeps all units consistent.
NASA and U.S. aerospace contractors frequently use Rankine in propulsion and thermal analysis. Rocket nozzle design, combustion chamber analysis, and atmospheric re-entry calculations all require absolute temperatures, and Rankine integrates with the imperial unit system used in many aerospace specifications.
The U.S. heating, ventilation, and air conditioning industry uses Fahrenheit for everyday measurements but needs absolute temperature for coefficient of performance (COP) calculations, refrigeration cycles, and heat pump efficiency analysis. Rankine bridges this gap seamlessly.
Students and researchers working between SI and imperial unit systems need to convert between Rankine and Kelvin regularly. Understanding the Rankine scale is essential for reading older U.S. engineering literature and for professional exams like the FE and PE.
This is the simplest conversion. Just add 459.67 to any Fahrenheit temperature to get Rankine, or subtract to go back. No multiplication needed.
If you know how Kelvin relates to Celsius (add 273.15), the same logic applies: Rankine relates to Fahrenheit (add 459.67). Both are absolute-scale versions of their respective relative scales.
Multiply Kelvin by 1.8 (or 9/5) to get Rankine. Since 273.15 K = 491.67 °R, and 491.67 / 273.15 = 1.8, this ratio holds at every temperature.
Rounding the offset to 460 introduces a 0.33-degree error on every conversion. In precision engineering, this can matter. Always use 459.67.
The Reaumur scale is a historical European scale where water freezes at 0 and boils at 80. It has nothing to do with Rankine. Watch for the accent mark: Réaumur vs Rankine.
If your calculation produces a negative Rankine number, there is an error. Rankine is an absolute scale; negative values are physically impossible, just like negative Kelvin.
The Rankine scale is an absolute thermodynamic temperature scale named after Scottish engineer William John Macquorn Rankine. Like Kelvin, it starts at absolute zero, but it uses Fahrenheit-sized degree increments instead of Celsius-sized ones. Zero Rankine (0 °R) equals absolute zero (-459.67 °F or 0 K).
Subtract 459.67 from the Rankine value. The formula is °F = °R - 459.67. For example, 671.67 °R (the boiling point of water) equals 671.67 - 459.67 = 212 °F.
Use the formula °C = (°R - 491.67) × 5/9. First subtract 491.67, then multiply by 5/9. For example, 491.67 °R equals (491.67 - 491.67) × 5/9 = 0 °C (the freezing point of water).
Multiply the Rankine value by 5/9. The formula is K = °R × 5/9. For example, 491.67 °R equals 491.67 × 5/9 = 273.15 K. The ratio 5/9 reflects the different degree sizes between Fahrenheit and Celsius families.
The Rankine scale was proposed in 1859 by William John Macquorn Rankine (1820–1872), a Scottish mechanical engineer and physicist at the University of Glasgow. Rankine was a founding contributor to thermodynamics and also developed the Rankine cycle used in steam engine and power plant analysis.
No. Because Rankine is an absolute scale starting at absolute zero, negative values are physically impossible. This is the same reason Kelvin cannot be negative. Absolute zero (0 °R = 0 K) represents the complete absence of thermal energy.
Engineers in the United States sometimes prefer Rankine because it pairs naturally with Fahrenheit, which is still the standard in U.S. industry for day-to-day temperature measurement. Using Rankine keeps absolute temperature calculations consistent with Fahrenheit pipe specs, material ratings, and equipment data.
Rankine and Kelvin are both absolute scales starting at absolute zero, but use different degree sizes. One Rankine degree equals one Fahrenheit degree (5/9 of a Kelvin). The conversion is °R = K × 9/5 or K = °R × 5/9. At absolute zero, both scales read zero.
This converter uses the standard offset of 459.67 for Rankine-Fahrenheit conversions and the exact ratio 5/9 for Rankine-Kelvin conversions. For mission-critical engineering calculations, always cross-check results with your organization's verified reference data and applicable standards (e.g., NIST, ASTM).