Celsius to Rankine Converter

1. Type the temperature in degrees Celsius. Negative values work down to -273.15, which is absolute zero.
2. Pick how many decimal places you want. Two is enough for most homework; property tables may need four.
3. Read the Rankine result, then the kelvin and Fahrenheit values below it. Paste a list into the bulk box to convert many readings at once.

In this guide, deg C means degrees Celsius, deg R means degrees Rankine and deg F means degrees Fahrenheit. The tool itself shows the degree sign.

A Celsius to Rankine conversion moves a temperature from the metric Celsius scale to the Rankine scale, an absolute scale that uses Fahrenheit-size degrees. It is the step you need when a reading taken in Celsius has to go into a formula written in US customary units.

The two scales differ in two ways at once. First, their zero points differ. Zero deg C is the old ice point, while 0 deg R is absolute zero. NIST SP 330 defines Celsius temperature as the thermodynamic temperature minus 273.15 K, so 0 deg C sits 273.15 K above absolute zero. Second, their degree sizes differ. NIST SP 811 gives T/K = (T/deg R) / 1.8, so one Rankine degree is 5/9 of a kelvin, and one kelvin equals one Celsius degree.

Most people who search this conversion are engineering students or technicians. A sensor, lab sheet or metric datasheet gives them Celsius, but their gas law, steam table or textbook problem uses deg R. NASA notes that the equation of state needs an absolute temperature, and that in the Imperial system this is Rankine, not Fahrenheit.

The formula first shifts Celsius to absolute zero by adding 273.15, then scales kelvin to Rankine by multiplying by 9/5.

1. Add 273.15 to the Celsius value. That gives kelvin. Example: 25 + 273.15 = 298.15 K.
2. Multiply by 9/5, which is exactly 1.8. Example: 298.15 x 1.8 = 536.67 deg R.
3. Check with the shortcut: 25 x 1.8 = 45, and 45 + 491.67 = 536.67 deg R.

The shortcut is not an approximation. The number 491.67 is simply 273.15 x 1.8, the Rankine value of the ice point. Both routes give identical results to every decimal, because every constant in them is exact by definition.

A lab at 25 deg C. (25 + 273.15) x 1.8 = 536.67 deg R. If a problem asks for air density at room conditions in pounds and feet, this is the temperature that goes into the gas law.

A standard day at 15 deg C. 15 x 1.8 + 491.67 = 518.67 deg R. NASA writes this sea-level standard as 518.6 in its Imperial atmosphere model, because it rounds 459.67 to 459.7 there.

Water boiling near 100 deg C. 100 x 1.8 + 491.67 = 671.67 deg R. The 100 Celsius degrees between ice and boiling become 180 Rankine degrees, from 491.67 to 671.67.

A cold night at -40 deg C. -40 x 1.8 + 491.67 = 419.67 deg R. The Rankine value is still well above zero, since -40 deg C is far warmer than absolute zero.

A furnace at 1,000 deg C. 1,000 x 1.8 + 491.67 = 2,291.67 deg R. Combustion and turbine problems in US units often land in the thousands of deg R.

To go the other way with any of these numbers, use the Rankine to Celsius converter, which starts from deg R.

The formula never changes, but four things decide how useful the number is.

Whether You Have a Temperature or a Temperature Change

A reading such as 25 deg C needs the full formula. A change such as a 10 deg C rise needs only the 1.8 factor: it equals an 18 deg R rise. Adding 491.67 to a change is wrong, and it is the most common error in heat-transfer homework.

The Resolution of the Celsius Reading

Each 0.1 deg C step in the input moves the answer by 0.18 deg R. A thermometer read to the nearest whole degree leaves about 0.9 deg R of doubt, so extra decimals in the output add no real accuracy.

Rounded Constants in Older Sources

Some books use 273 or 460 as round offsets. Using 273 instead of 273.15 shifts every answer down by 0.27 deg R. That is small for a quick estimate, but it breaks agreement with modern tables.

The Scale of the Original Data

Some sheets give readings in kelvin rather than Celsius. Entering kelvin as Celsius adds 491.67 deg R of error. Check the unit symbol first; for kelvin input, use the kelvin to Rankine page linked below.

You can reach Rankine from Celsius by way of kelvin or by way of Fahrenheit. Both are exact and give the same answer.

The kelvin value is also handy on its own. The Celsius to Kelvin converter covers that first step in more depth.

Gas Law Problems in US Units

The ideal gas law needs an absolute temperature. With pressure in pounds per square foot and density in slugs per cubic foot, that temperature must be in deg R. NASA writes the density of air as p divided by 1718 times (T + 459.7), which is the Rankine temperature.

Using US Property Tables with Metric Measurements

Specific heat and entropy in US engineering units are written per degree Rankine, such as Btu per pound per deg R. NIST SP 811 lists factors for these units. A Celsius measurement must become deg R before it meets such a table.

Thermal Efficiency Limits

The Carnot limit, 1 - T cold / T hot, only works with absolute temperatures. A plant with a 25 deg C sink and a 500 deg C source runs between 536.67 and 1,391.67 deg R, so the limit is about 61.4 percent. Plugging in Celsius values would give a wrong answer of 95 percent.

If your data starts in Fahrenheit, the Fahrenheit to Rankine converter needs only one addition.

Exact values from deg R = (deg C + 273.15) x 9/5, with kelvin for reference. Values are rounded to 2 decimals only where needed.

Every 10 deg C step adds exactly 18 deg R, so you can fill gaps in the chart by counting.

1. Adding 491.67 Without Multiplying First

25 + 491.67 gives 516.67, which is 20 deg R too low. The Celsius value must be scaled by 1.8 before the offset is added.

2. Using the Fahrenheit Offset with Celsius

459.67 belongs to Fahrenheit. Adding it to a Celsius value mixes two scales and gives nonsense, such as 484.67 for 25 deg C.

3. Multiplying by 1.8 and Then Adding 273.15

This applies the offset in the wrong units. For 25 deg C it gives 318.15, which is neither kelvin nor Rankine. Add 273.15 first, then multiply.

4. Converting a Temperature Change with the Offset

A 20 deg C rise is a 36 deg R rise. Only readings get the offset; differences only get the 1.8 factor.

5. Accepting Results Below Absolute Zero

No value below -273.15 deg C exists. A negative Rankine answer means the input or the scale is wrong. The tool blocks it.

The conversion is exact, because 273.15 and 9/5 are fixed by definition. Only the display is rounded, to the decimals you pick.

Zero degrees Celsius is 491.67 deg R. It is the ice point of water, 273.15 K above absolute zero, expressed in Fahrenheit-size degrees.

A room at 20 deg C is 527.67 deg R, and one at 25 deg C is 536.67 deg R. Each extra degree Celsius adds 1.8 deg R.

It is 273.15 multiplied by 1.8. That makes deg C x 1.8 + 491.67 the same exact formula as (deg C + 273.15) x 9/5, just in one step.

No. The famous -40 match is between Celsius and Fahrenheit. In Rankine, -40 deg C is 419.67 deg R.

Multiply the difference by 1.8 and add nothing. A 15 deg C rise equals a 27 deg R rise.

No real temperature can. The lowest Celsius value is -273.15, and that equals exactly 0 deg R. Lower inputs mean a typo or a wrong scale.

Use =A2*1.8+491.67 with the Celsius value in A2. The result is exact, and you can format the cell to the decimals you need.

Write deg R, or the degree sign with R. The Rankine unit keeps the word degree, unlike the kelvin, which is written K with no degree sign.

US property tables and many textbooks use pounds, feet and Btu. Those formulas need an absolute temperature with Fahrenheit-size degrees, and that is the Rankine scale.

No. The math runs in your browser. Saved results stay in your own browser storage until you clear them.

• Temperature conversion relations, including degree Rankine to kelvin (NIST SP 811, Appendix B.9).
• Definition of the kelvin and of Celsius temperature (NIST SP 330, The International System of Units, section 2).
• Exact temperature conversions and the Celsius degree as 1.8 Fahrenheit degrees (NIST Office of Weights and Measures).
• Absolute temperature in Rankine for the equation of state (NASA Glenn Research Center, Beginner's Guide to Aeronautics).