Rankine To Celsius Converter

1. Type the temperature in degrees Rankine, for example a value from a US property table. It cannot be below 0.
2. Set the decimal places. Rankine to Celsius rarely gives a short decimal, so 2 or 4 places are typical.
3. Read the Celsius value, then kelvin and Fahrenheit. To convert a whole table column, paste it into the bulk box.

In the text, deg R means degrees Rankine, deg C degrees Celsius and deg F degrees Fahrenheit. The tool prints the degree sign.

A Rankine to Celsius conversion turns an absolute temperature in Fahrenheit-size degrees into a metric reading measured from the ice point. People need it when data from US engineering sources has to be reported in metric units.

The Rankine scale is common in older US thermodynamics texts, steam and gas tables in English units, and aerospace models. NASA, for example, writes its Imperial standard atmosphere with (T + 459.7), which is the temperature in deg R. Celsius, by contrast, is the scale of most lab reports, weather data and international standards.

Two corrections are needed. The zero must move from absolute zero up to the ice point, which sits at 491.67 deg R. And the degree size must grow, since one Celsius degree equals 1.8 Rankine degrees. NIST SP 811 gives T/K = (T/deg R) / 1.8, and NIST SP 330 defines Celsius temperature as T - 273.15 K. Combining the two gives the formula below.

The formula removes the ice-point value in Rankine, then shrinks Rankine degrees into Celsius degrees by multiplying by 5/9.

1. Subtract 491.67. Example: 1,000 - 491.67 = 508.33.
2. Multiply by 5/9, or divide by 1.8. Example: 508.33 / 1.8 = 282.41 deg C.
3. Cross-check with the second route: 1,000 / 1.8 = 555.56 K, and 555.56 - 273.15 = 282.41 deg C.

The two routes always agree. The first is shorter on a calculator. The second is handy when you also want the kelvin value, which the tool shows anyway. The division by 1.8 is why most answers have repeating decimals: 1 deg R of difference is 0.5555... deg C.

A standard day, 518.67 deg R. (518.67 - 491.67) x 5/9 = 27 x 5/9 = 15 deg C. This is the sea-level standard temperature, 59 deg F.

A table entry at 1,000 deg R. (1,000 - 491.67) x 5/9 = 282.41 deg C. Round Rankine values in US gas tables rarely give round Celsius values.

Hot gas at 2,000 deg R. (2,000 - 491.67) x 5/9 = 837.96 deg C.

The lower stratosphere. NASA holds this layer at -70 deg F in its Imperial model. That is 389.67 deg R, and (389.67 - 491.67) x 5/9 = -56.67 deg C.

Zero Fahrenheit, 459.67 deg R. (459.67 - 491.67) x 5/9 = -32 x 5/9 = -17.78 deg C.

Absolute zero, 0 deg R. (0 - 491.67) x 5/9 = -273.15 deg C, the lowest Celsius value that exists.

To take a Celsius value back to Rankine, open the Celsius to Rankine converter.

The math is fixed, yet these four points decide whether the answer is right for your task.

Reading Versus Difference

A Rankine reading needs the 491.67 offset. A Rankine difference does not. A table step of 100 deg R is a 55.56 deg C step, not -217.59 deg C.

The Offset the Source Used

Older US sources and some NASA models round 459.67 to 459.7. That shifts the implied Celsius value by about 0.017 deg C. It rarely matters, but it explains small mismatches between tables.

Rounding in the Rankine Data

A table value given to the nearest whole deg R carries up to 0.5 deg R of rounding. That becomes about 0.28 deg C. Showing 6 decimals in the answer does not remove that doubt.

Whether the Value Is Really Rankine

Rankine and Fahrenheit share the same degree size, so a Fahrenheit number can hide in a Rankine column. Any value below about 400 in a room-temperature context should make you check the unit.

From Rankine, Fahrenheit is one subtraction away, while Celsius needs a subtraction and a scale change.

When a US audience reads your result, the Rankine to Fahrenheit converter is the shorter path.

Reporting US Table Data in Metric

A steam or gas table in English units may list 1,260 deg R. A metric report needs 426.85 deg C. Pasting the table column into the bulk box converts it in one step.

Reading Aerospace Models Written in Imperial Units

NASA's Imperial atmosphere model gives 23.4 deg F at 10,000 ft, which is 483.07 deg R. In Celsius that is -4.78 deg C, easier to compare with metric weather data.

Checking Homework Answers

Many US textbook problems finish in deg R. Converting the answer to Celsius gives a quick sense check: a problem about air in a room should end near 20 to 25 deg C, which is 527.67 to 536.67 deg R.

When the result should stay absolute for SI work, the kelvin to Celsius converter covers the last step from K.

Exact values from deg C = (deg R - 491.67) x 5/9, rounded to 2 decimals, with Fahrenheit for reference.

Every 9 deg R step moves the Celsius value by exactly 5 deg C, which helps when you fill gaps by hand.

1. Subtracting 459.67 and Stopping

That gives Fahrenheit, not Celsius. For 1,000 deg R it returns 540.33, which is deg F.

2. Subtracting 273.15 from the Rankine Number

273.15 is a kelvin offset. (1,000 - 273.15) x 5/9 gives 403.81, about 121 degrees too high.

3. Multiplying by 9/5 Instead of 5/9

The Celsius number must be smaller than the Rankine difference, not larger. Using 9/5 inflates the answer by a factor of 3.24.

4. Rounding 5/9 to 0.55 or 0.56

At 1,000 deg R, 0.55 gives 279.58 deg C and 0.56 gives 284.66 deg C. The exact answer is 282.41 deg C. Divide by 1.8 instead.

5. Using the Offset on a Temperature Change

A 90 deg R change is a 50 deg C change. Only full readings get the 491.67 shift.

The conversion is exact, because 491.67 and 5/9 come from defined constants. The display rounds only to the decimals you pick.

500 deg R is 4.63 deg C. Subtract 491.67 to get 8.33, then multiply by 5/9.

It is 491.67 deg R, the ice point. Rankine values above 491.67 give positive Celsius answers, and values below it give negative ones.

It is about 282.41 deg C. The exact value is 282.40555... deg C, since the division by 1.8 repeats.

Yes. Any value between 0 and 491.67 deg R is below 0 deg C. For example, 400 deg R is -50.93 deg C.

Rankine to Celsius divides by 1.8, which often repeats forever. Only Rankine values that are a multiple of 9 above 491.67 give whole Celsius numbers.

Kelvin is usually faster: divide by 1.8, then subtract 273.15. Going through Fahrenheit needs a subtraction, a second subtraction and a division.

Multiply the difference by 5/9 and apply no offset. A 36 deg R difference equals a 20 deg C difference.

Use =(A2-491.67)/1.8 with the Rankine value in A2, then set the number format to the decimals you need.

US engineering formulas in pounds, feet and Btu need an absolute temperature with Fahrenheit-size degrees. NASA notes that Rankine is the absolute temperature of the Imperial system.

No. The page does the math locally. The Save button writes only to your own browser, and Clear removes it.

• Temperature conversion relations for Rankine, kelvin and Celsius (NIST SP 811, Appendix B.9).
• Celsius temperature defined as T - 273.15 K (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).
• Imperial standard atmosphere written with T + 459.7 (NASA Glenn Research Center, Earth Atmosphere Model).
• Rankine as the absolute temperature of the Imperial system (NASA Glenn Research Center, Equation of State).