Rankine To Kelvin Converter

1. Enter the temperature in degrees Rankine. The value must be 0 or more, because 0 deg R is absolute zero.
2. Choose the decimal places. Use 4 or more when the kelvin value feeds another calculation.
3. Read the kelvin result, then Celsius and Fahrenheit. For a data set, paste the Rankine column into the bulk box.

On this page, deg R is degrees Rankine, deg C is degrees Celsius and deg F is degrees Fahrenheit. Kelvin is written K, with no degree sign.

A Rankine to kelvin conversion moves an absolute temperature from US customary units into the SI unit of thermodynamic temperature by multiplying by 5/9. It is the step that makes English-unit engineering data usable in SI equations.

The two scales share one zero, absolute zero, and differ only in degree size. NIST SP 811 states T/K = (T/deg R) / 1.8 and lists one Rankine degree of interval as 5.555 556 x 10^-1 K, which is 5/9 K. NIST SP 330 defines the kelvin itself by fixing the Boltzmann constant, so the kelvin side of the relation is exact.

Rankine values usually come from US sources: thermodynamics texts in English units, property data written per degree Rankine, and aerospace models. Kelvin is what SI software, international papers and most physics formulas expect. Converting also makes it easy to compare a US source with a metric one line by line.

The formula divides the Rankine value by 1.8, because a kelvin is 1.8 times larger than a Rankine degree.

1. Take the Rankine value. Example: 540 deg R.
2. Divide by 1.8, or multiply by 5 and divide by 9. Example: 540 x 5 = 2,700, and 2,700 / 9 = 300 K.
3. Check by multiplying back: 300 x 1.8 = 540 deg R.

The multiply-by-5, divide-by-9 order is handy by hand. Any Rankine value that is a multiple of 9 gives a whole number of kelvins: 9 deg R is 5 K and 180 deg R is 100 K. Other values give repeating decimals, so the tool lets you pick the precision.

Room air at 540 deg R. 540 / 1.8 = 300 K. That is 26.85 deg C, a warm room.

The ice point, 491.67 deg R. 491.67 / 1.8 = 273.15 K, exactly 0 deg C.

A standard day, 518.67 deg R. 518.67 / 1.8 = 288.15 K. NASA writes 518.6 in its Imperial model; that rounded value gives 288.11 K.

Combustion gas at 1,800 deg R. 1,800 / 1.8 = 1,000 K. Values in the thousands of deg R turn into neat kelvin numbers when they are multiples of 9.

A table value of 1,000 deg R. 1,000 x 5/9 = 555.556 K, a repeating decimal.

A cold gas at 180 deg R. 180 / 1.8 = 100 K, which is -173.15 deg C.

To send an SI temperature back to US units, the kelvin to Rankine converter multiplies by 1.8.

A single factor does the work, but four details decide whether the answer fits your problem.

Precision of the Rankine Data

Dividing by 1.8 shrinks any uncertainty too. A value known to plus or minus 1 deg R gives kelvin known to plus or minus 0.56 K.

Whether the Number Is Rankine or Fahrenheit

A Fahrenheit value typed as Rankine gives a result far too cold. 80 deg F entered as 80 deg R returns 44.44 K instead of 299.82 K. Check the column heading in the source.

Rounded Offsets in the Source

Some US sources write 459.7 or 460 when they build Rankine values from Fahrenheit. Using 460 adds 0.33 deg R, which becomes 0.18 K after conversion.

Units That Carry Temperature Inside Them

Specific heat per deg R and per K differ by the same 5/9 idea. NIST SP 811 gives 1 Btu per pound per deg R as 4,186.8 J per kilogram per K. Convert the temperature and the property with matching factors.

The exact factor is 5/9, a repeating decimal. Rounded versions save typing but add error, as this table shows for 1,000 deg R.

Dividing by 1.8 is exact and just as quick, so there is little reason to round. For the Celsius step after kelvin, the kelvin to Celsius converter subtracts 273.15.

Running SI Software with US Data

Simulation tools and SI formulas expect kelvin. A US test report at 630 deg R becomes 350 K before it goes in.

Comparing US and Metric Property Tables

An English-unit table at 720 deg R lines up with an SI table at 400 K. Converting the Rankine column lets you check that both sources agree.

Physics Formulas That Need Kelvin

Gas laws and radiation formulas use thermodynamic temperature. NASA notes that the equation of state needs an absolute scale, which is kelvin in metric work and Rankine in Imperial work. Converting Rankine to kelvin lets you use SI constants without mixing units.

If your starting value is in Fahrenheit, first use the Fahrenheit to Rankine converter, then return here.

Values from K = deg R x 5/9, exact to 3 decimals, with Celsius for reference.

Each 9 deg R step adds exactly 5 K, so rows at multiples of 9 are whole kelvins.

1. Multiplying by 1.8 Instead of Dividing

The kelvin number is always the smaller one. 540 x 1.8 gives 972, which is the wrong direction.

2. Subtracting 459.67 First

That turns the value into Fahrenheit. 540 - 459.67 = 80.33, and 80.33 x 5/9 = 44.63, which is neither kelvin nor Celsius.

3. Subtracting 273.15 from the Rankine Value

273.15 belongs to the Celsius and kelvin pair. It has no place between Rankine and kelvin.

4. Rounding 5/9 to 0.55

That makes every answer 1 percent too low, about 5.6 K at 1,000 deg R. Divide by 1.8 for an exact result.

5. Writing the Answer as Degrees Kelvin

The SI unit is simply the kelvin, symbol K. Keep the degree sign for deg R, deg C and deg F only.

The result is exact, because 5/9 is a defined ratio. Only the display is rounded, to the decimals you choose.

It is 333.333 K. Divide 600 by 1.8; the result repeats, so round it to the precision you need.

Yes. Both mark absolute zero. That shared zero is why the conversion needs no offset.

One Rankine degree is 5/9 K, about 0.5556 K. NIST SP 811 lists it as 5.555 556 x 10 to the power -1 K.

Multiples of 9 do. For example, 9 deg R is 5 K, 900 deg R is 500 K and 2,700 deg R is 1,500 K.

A kelvin is a bigger step than a Rankine degree, 1.8 times bigger. It takes fewer kelvins to cover the same distance from absolute zero.

Use the same 5/9 factor. A 45 deg R change is a 25 K change. Between these two scales, readings and changes convert the same way.

Not directly. Add 459.67 to get Rankine first, then divide by 1.8. NIST SP 811 writes this as T/K = (t/deg F + 459.67) / 1.8.

Use =A2/1.8 with the Rankine value in A2. Division by 1.8 is exact, unlike a rounded 0.5556 factor.

Mostly in US engineering: thermodynamics texts in English units, property data written per degree Rankine, and aerospace models such as the NASA Imperial atmosphere.

No. It all runs on your device, and saved results sit in your browser until you clear them.

• Degree Rankine to kelvin and the Rankine interval of 5/9 K (NIST SP 811, Appendix B.8).
• Temperature relations, including Fahrenheit to kelvin (NIST SP 811, Appendix B.9).
• Definition of the kelvin, the SI unit of thermodynamic temperature (NIST SP 330, The International System of Units, section 2).
• Absolute temperature in kelvin or Rankine for the equation of state (NASA Glenn Research Center, Equation of State).
• Imperial standard atmosphere with a 518.6 deg R reference (NASA Glenn Research Center, Earth Atmosphere Model).