Celsius to Rankine Converter
Convert Celsius to Rankine by first adding 273.15 to get Kelvin, then multiplying by 1.8. The combined formula is °R = (°C + 273.15) × 1.8, equivalent to °R = °C × 1.8 + 491.67....
Formula
Source: NIST ITS-90, ISO 80000-5 (Quantities and units, Thermodynamics) | Last reviewed: June 27, 2026
Examples
0 °C
= 491.67 °R
Freezing point of water, 0 °C = 273.15 K = 491.67 °R
20 °C
= 527.67 °R
Standard room temperature, 20 °C = 293.15 K = 527.67 °R (CAGI/ASHRAE 20 °C reference)
100 °C
= 671.67 °R
Boiling point of water at 1 atm
500 °C
= 1391.67 °R
High-temperature industrial process, 500 °C = 773.15 K = 1,391.67 °R
-273.15 °C
= 0 °R
Absolute zero, 0 °R by definition
Quick Reference Table
| °C | K | °R | Reference |
|---|---|---|---|
| -273.15 | 0 | 0 | Absolute zero |
| -196 | 77.15 | 138.87 | Liquid nitrogen saturation |
| -162 | 111.15 | 200.07 | LNG saturation (methane at 1 atm) |
| -40 | 233.15 | 419.67 | Cold-climate design reference (−40 °F = −40 °C) |
| 0 | 273.15 | 491.67 | Water freezing point |
| 20 | 293.15 | 527.67 | Standard room temperature |
| 37 | 310.15 | 558.27 | Human body temperature |
| 100 | 373.15 | 671.67 | Water boiling point at 1 atm |
| 200 | 473.15 | 851.67 | Saturated steam at ~225 psig |
| 315 | 588.15 | 1058.67 | PWR nuclear reactor outlet temperature |
| 538 | 811.15 | 1460.07 | Ultra-supercritical steam (some plants) |
| 816 | 1089.15 | 1960.47 | Ultra-supercritical advanced steam |
| 1500 | 1773.15 | 3191.67 | High-temperature process / turbine inlet region |
Where is this used?
The combined formula is °R = (°C + 273.15) × 1.8, which is algebraically equivalent to °R = °C × 1.8 + 491.67.
This conversion appears when metric-temperature equipment data (°C) from European or Asian manufacturers must be used in US thermodynamic calculations that require absolute temperature in °R.
The two-step nature of the conversion, add 273.15, then multiply by 1.8, makes it slightly more error-prone than the pure-multiplication K-to-°R conversion, and the order of operations matters (the addition must happen before the multiplication because the offset 273.15 is in Celsius units, which are 1.8× larger than Fahrenheit units).
A common mistake is to multiply °C by 1.8 first (getting 1.8 × °C) and then add 491.67, this is algebraically correct but requires remembering 491.67 instead of 273.15, and the intermediate 1.8 × °C value has no physical meaning.
The safer mental workflow is to add 273.15 first to get Kelvin (a physically meaningful absolute temperature), then multiply by 1.8 to get Rankine.
This two-step approach has the advantage that the intermediate Kelvin value can be sanity-checked against known reference points (0 °C → 273.15 K, 100 °C → 373.15 K) before the second conversion.
The Celsius-to-Rankine conversion is increasingly common as European and Asian manufacturers penetrate US markets with equipment specified in °C.
For example, a German MAN Energy Solutions compressor datasheet specifies the suction temperature as 25 °C and the discharge temperature as 145 °C, the US process engineer converting these to °R for the plant's heat balance obtains 536.67 °R (suction) and 752.67 °R (discharge), a temperature rise of 216 °R (120 K) that determines the compressor's isentropic efficiency calculation.
In the LNG industry, where Bechtel (US), Chiyoda (Japan), JGC (Japan), Technip Energies (France), and Saipem (Italy) all bid on the same projects, the pre-FEED (front-end engineering design) heat and material balances may arrive in mixed units, the French contractor's main cryogenic heat exchanger (MCHE) specification in °C and K, while the US owner's existing plant documentation is in °F and °R.
The project's unit conversion protocol must be rigorously defined in the basis of design (BOD) document to prevent the kind of systematic error that occurs when one discipline converts correctly and another doesn't.
The Mars Climate Orbiter failure in 1999, caused by one team using SI (Newton-seconds) and another using US customary (pound-force-seconds) for the same thruster impulse data, is the canonical warning.
Temperature is equally vulnerable: a heat exchanger designed for 500 °C (932 °F, 1,391.67 °R) process fluid that is mistakenly treated as 500 °F (260 °C, 959.67 °R) would be undersized by 45% in the temperature driving force, a catastrophic design error.
Where °C-to-°R conversions appear in real engineering work.
International LNG plant design and construction: Modern LNG plants (mega-trains of 5+ MTPA capacity) are typically designed by international consortia.
The liquefaction process (APCI C3MR, ConocoPhillips Optimized Cascade, Linde MFC, Air Products AP-X) has a mixed temperature range from ambient (35 °C sea-level design temperature for the Gulf Coast, 45 °C for Middle East summer) to cryogenic (−162 °C LNG product).
The proprietary process design is performed in SI by the licensor (Air Products, ConocoPhillips, Shell, Linde), with detailed engineering performed by EPC contractors in mixed units.
A US-based EPC contractor (Bechtel, KBR, CB&I/McDermott) converting the licensor's SI heat balance to US customary for procurement and construction applies the °C-to-°R conversion to every state point: from the inlet gas reception (35 °C = 308.15 K = 554.67 °R) through the propane pre-cooling (−35 °C = 238.15 K = 428.67 °R), the mixed-refrigerant cooling (−100 °C = 173.15 K = 311.67 °R), and finally the LNG product (−162 °C = 111.15 K = 200.07 °R).
An error in any of these conversions propagates through the entire process simulation.
International compressor and turbine procurement: Major rotating equipment (compressors, turbines, pumps) is now globally sourced.
A US refinery replacing an obsolete compressor might receive bids from Siemens (Germany), MAN (Germany), Atlas Copco (Sweden), Elliott (Japan/Korea), and Solar Turbines (US).
The non-US bids specify performance in °C and K; the US bid specifies °F and °R.
The engineering team converts the °C and K values to °R for direct comparison: a compressor with suction at 35 °C (308.15 K = 554.67 °R) and discharge at 145 °C (418.15 K = 752.67 °R) provides a temperature rise of 198 °R (110 K).
The efficiency comparison is done on a common basis after the °R conversion.
A 1 °C error in the suction temperature (1.8 °R error) translates to about 1% error in the polytropic head calculation, which is above the typical procurement tolerance (±0.5% for centrifugal compressor performance).
International research collaboration: Engineering research increasingly involves international teams.
A heat transfer research project between MIT and ETH Zurich (Swiss Federal Institute of Technology) might specify experimental conditions in °C (Swiss standard) and report results in °R (US standard).
The °C-to-°R conversion is applied to every experimental data point and every simulation output.
A 1 °C error (1.8 °R error) in the experimental temperature measurement corresponds to a 1-2% error in the measured heat transfer coefficient, depending on the heat transfer mode, meaningful for the validity of the published research results.
Nuclear power plant design: Modern nuclear power plants (Generation III+ and Generation IV designs) are designed by international teams.
The AP1000 (Westinghouse), EPR (Framatome/Areva), Hualong One (China National Nuclear Corporation), and VVER-1200 (Russian) designs all use SI internally, but US license applications and NRC safety analysis reports must present data in customary units.
The reactor coolant temperatures (typical PWR: 290-325 °C, BWR: 215-285 °C) are converted from °C to °R for the US safety analysis: 325 °C = 598.15 K = 1,076.67 °R.
The fuel centerline temperature limit (typical 1,800 °C for UO₂ fuel) = 2,073.15 K = 3,531.67 °R.
The conversion must be exact for the safety analysis, an error in the temperature conversion could produce an off-by-tens-of-degrees error in the safety analysis report, potentially failing NRC review.
Real-World Usage Scenarios
US LNG receiving terminal expansion (international engineering)
An existing LNG receiving terminal in the US Gulf Coast plans to add a third vaporization train. The new train uses the IPSMR (Integrated Pre-cooled Single Mixed Refrigerant) process licensed by Chart Industries. The process design package (PDP) from Chart specifies all temperatures in °C: pre-cooling at −30 °C, main liquefaction heat exchange at −100 °C, and LNG storage at −162 °C. The US engineering firm (Burns & McDonnell) is contracted for detailed engineering and converts all PDP temperatures to °F and °R for the US design package. The conversion is applied at every state point. A 1 °C error in any conversion (1.8 °R error) translates to about 0.5-1% error in the corresponding heat transfer or compressor calculation, potentially affecting the predicted vaporization capacity and the terminal's throughput guarantee.
International gas turbine acceptance test
A Korean utility purchases a GE 9HA gas turbine. The acceptance test is conducted at GE's Greenville, SC facility per ASME PTC 22. The turbine performance is measured at various load points, with the turbine inlet temperature (TIT) measured directly by the GE test instrumentation in °F. The test report is delivered to the Korean utility in their preferred units (°C and K) for their power plant performance monitoring. The conversion °F → °R → K is applied to every test data point. The Korean utility's engineers, working in their native °C/K system, must verify the test data matches their contractual specifications. A 1 °F error in the TIT reading (0.56 K error) translates to about 0.5% error in the heat rate prediction, which could trigger a contractual dispute if the heat rate exceeds the guarantee.
European heat pump installation in US building
A US building owner installs a European-manufactured air-source heat pump (Daikin Altherma 3, manufactured in Belgium). The equipment performance is specified in °C at standard rating conditions (A7/W35 per EN 14511: −7 °C outdoor, 35 °C indoor water, heating capacity 16 kW). The US HVAC engineer converts the performance data to °F and °R for integration with the building's Manual J heating load calculation (expressed in °F and BTU/hr). The conversion is performed at every rating point. The capacity at A7/W35 (heating mode) is 16 kW × 3,412 = 54,600 BTU/hr (≈ 4.5 tons), which matches the building's heating load at the design outdoor temperature (−7 °C = 19.4 °F = 479.07 °R). The conversion accuracy directly affects whether the selected equipment matches the building load.
Industry Standards Referenced
Frequently Asked Questions
Do I add 273.15 first or multiply by 1.8 first?
Add 273.15 first, then multiply by 1.8. Or equivalently, multiply °C by 1.8 and add 491.67 (since 273.15 × 1.8 = 491.67). Both are algebraically identical. The add-then-multiply sequence is easier to remember because the intermediate value (Kelvin) has physical meaning and known reference points for sanity checking. The multiply-then-add sequence requires remembering the less-commonly-used 491.67 offset. Whatever you do, do NOT multiply by 1.8, add 273.15, and multiply by 1.8 again, that's a double conversion that produces nonsense values far from reality.
Why does the formula use 273.15 instead of 273?
The exact definition of absolute zero relative to the Celsius scale is −273.15 °C, established by the International Temperature Scale of 1990 (ITS-90). Before 1990 (and in many older textbooks), the value −273.15 was also used in IPTS-68. Using 273 instead of 273.15 introduces an error of 0.15 °C (0.27 °R), negligible for most industrial purposes (0.05% error at room temperature) but significant in cryogenic applications (it's a 0.2% error at liquid nitrogen temperature of 77 K). For industrial HVAC, process heating, and power generation calculations, 273 is acceptable for quick estimates. For published work, use 273.15 to conform to ITS-90.
What's the difference between °C-to-°R and °C-to-K?
Both convert a relative temperature to an absolute temperature. The difference is in the resulting scale: K (Kelvin) is the SI absolute scale with the same degree size as Celsius (1 K = 1 °C); °R (Rankine) is the US absolute scale with the same degree size as Fahrenheit (1 °R = 1 °F). The K-to-°R conversion is just × 1.8 (since 1 K = 1.8 °R), so the question of which absolute scale to use depends entirely on the unit system of the rest of your calculation. If your gas constant R is in J/(mol·K), use K. If R is in ft·lbf/(lbmol·°R), use °R. Mixing them produces errors: using K with the US specific gas constant for air (53.35 ft·lbf/(lbm·°R)) gives a PV = mRT result off by a factor of 1.8.
How accurate is the conversion at very high temperatures?
The °C-to-°R conversion is exact (within ITS-90 precision) at all temperatures. At very high temperatures (above 1,000 °C), the conversion is still straightforward, a 1,500 °C furnace temperature converts to (1,500 + 273.15) × 1.8 = 3,191.67 °R. The challenge at very high temperatures isn't the conversion itself but the measurement: optical pyrometers and radiation thermometers have larger uncertainties at higher temperatures, so the practical precision of the converted value is limited by the measurement precision.
How does this conversion interact with the ITS-90 temperature scale?
The ITS-90 defines absolute temperature via a series of fixed points (triple points, freezing points, and boiling points of pure substances) and the interpolating instruments (platinum resistance thermometers, gas thermometers, radiation thermometers). The fixed-point temperatures are defined exactly, and the conversion between °C and K is by definition (273.15 offset). The K-to-°R conversion (× 1.8) preserves the absolute zero and is exact. For precision work (better than 0.001 °R), consult NIST ITS-90 fixed-point data directly. For all engineering work, the simplified conversion in this calculator is sufficient and is consistent with NIST SP 811.
Reviewed for accuracy
Verified against ITS-90 definitions and standard thermodynamic reference points · Last reviewed: June 27, 2026
All calculations are for reference only. Always verify with manufacturer data and a qualified engineer for critical applications. Learn about our editorial process.