Fahrenheit to Rankine Converter

1. Type the temperature in degrees Fahrenheit. Negative values are fine down to -459.67, which is absolute zero.
2. Set the decimal places. Two places are enough for most work, because the offset 459.67 has two decimals.
3. Read the Rankine value, then Celsius and kelvin. To convert many readings, paste them into the bulk box.

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

A Fahrenheit to Rankine conversion turns an everyday US temperature reading into an absolute temperature. An absolute temperature starts at absolute zero, the lowest temperature that exists.

Fahrenheit is a relative scale. Its zero is an arbitrary point, so 80 deg F is not twice as hot as 40 deg F. Rankine fixes that. It keeps the Fahrenheit degree size and moves the zero down to absolute zero. NASA describes it as the absolute temperature that corresponds to the Fahrenheit degree.

The conversion matters in US engineering formulas. Gas laws, the equation of state and many heat formulas need an absolute temperature. NASA notes that in the Imperial system the absolute temperature is in Rankine, not degrees Fahrenheit. Students in thermodynamics, HVAC technicians and aerospace engineers make this conversion as the first step of a larger calculation.

The conversion is not a change of unit size. That is the main difference from Fahrenheit to Celsius or Fahrenheit to kelvin, which both divide by 1.8.

The formula adds one constant, 459.67, to the Fahrenheit reading. That constant is the distance from absolute zero up to 0 deg F, counted in Fahrenheit-size degrees.

1. Write down the Fahrenheit reading. Example: 70 deg F.
2. Add 459.67. Example: 70 + 459.67 = 529.67 deg R.
3. Check that the answer is not negative. A negative Rankine value means the input was below absolute zero.

The offset comes from two NIST relations. NIST SP 811 gives T/K = (t/deg F + 459.67) / 1.8 for Fahrenheit and T/K = (T/deg R) / 1.8 for Rankine. Setting the two equal removes the 1.8 and leaves deg R = deg F + 459.67. The same number also follows from the ice point: 273.15 K x 1.8 = 491.67 deg R, and 491.67 - 32 = 459.67.

A standard day, 59 deg F. 59 + 459.67 = 518.67 deg R. This is the sea-level temperature in the NASA standard atmosphere, equal to 15 deg C and 288.15 K.

Room temperature, 70 deg F. 70 + 459.67 = 529.67 deg R.

Water boiling at 1 atm, 212 deg F. 212 + 459.67 = 671.67 deg R.

A cold reading, -40 deg F. -40 + 459.67 = 419.67 deg R. Negative Fahrenheit readings still give positive Rankine values.

The lower stratosphere, -70 deg F. NASA holds this layer at -70 deg F in its Imperial model. -70 + 459.67 = 389.67 deg R.

Absolute zero, -459.67 deg F. -459.67 + 459.67 = 0 deg R, the lowest value on the scale.

To take a Rankine value back to Fahrenheit, open the Rankine to Fahrenheit converter in the related tools below, or switch the direction box above.

The math is one addition, yet these four points decide whether the answer suits your task.

The Offset the Source Used

NIST uses 459.67. Some references round it. NASA writes its Imperial atmosphere model with T + 459.7, and one NASA teaching page gives R = F + 459.69. Those choices shift the answer by 0.03 and 0.02 deg R. The gap is small, but it explains mismatches in the last digit.

Reading Versus Difference

A Fahrenheit reading needs the offset. A Fahrenheit difference does not. A rise of 25 deg F is a rise of 25 deg R, not 484.67 deg R.

Precision of the Thermometer

A reading taken to the nearest whole degree carries up to 0.5 deg F of doubt. The Rankine value carries the same 0.5 deg R. Showing 8 decimals does not remove it.

Whether the Input Is Really Fahrenheit

A Celsius reading typed as Fahrenheit gives a wrong but believable answer. 20 deg C entered as 20 deg F returns 479.67 deg R, while the true value is 527.67 deg R. For Celsius readings, convert with the Celsius to Fahrenheit converter first.

Both conversions give an absolute temperature. Rankine keeps Fahrenheit-size degrees, while kelvin switches to Celsius-size degrees.

Pick Rankine when the rest of the formula uses pounds, feet and Btu. Pick kelvin when the formula uses SI units. The Fahrenheit to kelvin converter covers the SI route. For weather or cooking, the Fahrenheit to Celsius converter is the right tool, since neither task needs an absolute scale.

Gas Law Problems in US Units

Gas laws use ratios of absolute temperature. Air in a rigid tank warmed from 70 deg F to 120 deg F goes from 529.67 to 579.67 deg R. The absolute pressure rises by 579.67 / 529.67 = 1.0944, or about 9.4 percent. Using the Fahrenheit numbers gives 120 / 70 = 1.71, which is wrong.

Air Density from the Equation of State

NASA gives air density in Imperial units as r = p / [1718 x (T + 459.7)], with T in deg F. The bracket is the Rankine temperature. At 59 deg F and 2,116 pounds per square foot, the density is about 0.00237 slug per cubic foot.

Preparing a Column of Readings

Field logs are in Fahrenheit, but a spreadsheet model may need Rankine. Paste the column into the bulk box and copy the converted list.

When a later step needs SI units, the kelvin to Celsius converter handles the last metric step.

Exact values from deg R = deg F + 459.67, with kelvin rounded to 2 decimals for reference.

Every row differs from its Fahrenheit value by the same 459.67. That constant gap is the quickest way to spot a typing error in a table.

1. Multiplying by 1.8 or 9/5

That step belongs to Celsius and kelvin conversions. Fahrenheit and Rankine degrees are the same size. 70 x 1.8 + 459.67 gives 585.67, which is 56 degrees too high.

2. Adding 273.15

273.15 is the Celsius to kelvin offset. 70 + 273.15 = 343.15 is neither Rankine nor kelvin for a 70 deg F reading.

3. Adding 491.67

491.67 deg R is the ice point, used when Celsius is involved. Adding it to a Fahrenheit value overshoots by exactly 32 degrees.

4. Using Fahrenheit Directly in a Ratio

Ratios only work on absolute scales. 80 deg F is not double 40 deg F. In Rankine the ratio is 539.67 / 499.67 = 1.08.

5. Applying the Offset to a Temperature Rise

A 10 deg F rise is a 10 deg R rise. Only full readings get the 459.67 shift.

6. Rounding to 460 Without Saying So

Adding 460 is a handy mental shortcut. It runs 0.33 deg R high, about 0.06 percent at room temperature. State the shortcut when the result goes into a report.

The conversion is exact, because 459.67 follows from defined constants. The display rounds only to the decimals you pick.

0 deg F is 459.67 deg R. The offset itself is the Rankine value of zero Fahrenheit.

100 deg F is 559.67 deg R. Add 459.67 to the Fahrenheit reading and change nothing else.

It is 558.27 deg R. The same temperature is 37 deg C and 310.15 K.

No. Rankine starts at absolute zero, so every real temperature is 0 deg R or higher. A negative answer means the Fahrenheit input was below -459.67.

The ice point is 273.15 K, which is 491.67 deg R, and it sits at 32 deg F. Subtracting 32 from 491.67 leaves 459.67. The value 460 is only a rounded shortcut.

Use Rankine when the formula is in pounds, feet and Btu, and kelvin when it is in SI units. Both are absolute scales, so either works when the constants match.

Use =A2+459.67 with the Fahrenheit value in A2. Fill the formula down the column to convert a whole log.

Yes. A change of 1 deg F equals a change of 1 deg R. Only the zero points differ.

The book probably added 459.7 instead of 459.67. Older references and some NASA models use the rounded offset.

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

• Temperature conversion relations for Fahrenheit, Rankine and kelvin (NIST SP 811, Appendix B.9).
• Exact temperature conversions and the Celsius degree as 1.8 Fahrenheit degrees (NIST Office of Weights and Measures).
• Rankine as the absolute scale that matches the Fahrenheit degree (NASA Glenn Research Center, Gas Temperature).
• Absolute temperature in the equation of state: Rankine in the Imperial system (NASA Glenn Research Center, Equation of State).
• Imperial standard atmosphere written with T + 459.7 (NASA Glenn Research Center, Earth Atmosphere Model).