Fahrenheit to Rankine Converter

Common questions

What is the formula for Fahrenheit to Rankine?

Rankine = Fahrenheit + 459.67. There is no multiplication in it, because a Rankine degree and a Fahrenheit degree are the same size: only the zero point moves. So 0 °F is 459.67 °R, 32 °F is 491.67 °R, 70 °F is 529.67 °R, 212 °F is 671.67 °R and 1,000 °F is 1,459.67 °R. Every answer on this page ends in .67 when the Fahrenheit reading is a whole number, which is a quick way to check you read the right line.

Why is this the only temperature conversion that is just an offset?

Because the other pairs change the size of the degree as well as the zero. Celsius and Kelvin share a degree size too, but they are the metric pair: K = C + 273.15. Fahrenheit and Rankine are the customary pair, and a Fahrenheit degree is 5/9 of a kelvin, so converting Fahrenheit to Celsius or to Kelvin needs both a multiplication and an addition. Fahrenheit to Rankine needs only the addition, which is why it can be done in your head.

Who actually uses Rankine?

Engineers working in US customary units when the physics needs an absolute temperature. The ideal gas law, thermal efficiency ratios and the Stefan-Boltzmann radiation law all take a temperature that starts at absolute zero, so a combustion, gas turbine, refrigeration or HVAC calculation carried out in Btu, psia and °F uses °R rather than °F for those steps. The scale is named after William John Macquorn Rankine, the Glasgow engineer who proposed it in 1859, and it is written °R.

Where is Rankine in this converter, and why is it called uncommon?

Both unit menus, From and To, list all four temperature scales, so Rankine is selectable from either side, and this page arrives with it already chosen on the right. The list underneath the converter is the part that hides it: that list shows the common units only, which for temperature means Celsius and Kelvin, until you tick Uncommon units, Show 1 more, in the strip under the stage. Turn it on and Rankine appears in the list as well. The switch remembers its state for your next visit.

Is the number exact, or is it rounded?

The definition is exact: 459.67 is a defined offset, not a measurement, so R = F + 459.67 carries no error. The display rounds to twelve significant digits, which is far more than any thermometer justifies and enough to absorb the floating-point residue left by converting through kelvin internally. One case shows that residue plainly: type -459.67 °F, which is absolute zero, and the answer reads -5.115908e-14 instead of a clean 0. Read that as zero. Coming the other way it lands exactly: 0 °R gives -459.67 °F.

How do I convert Rankine back to Fahrenheit, or reach it from Celsius and Kelvin?

Subtract: Fahrenheit = Rankine - 459.67. The swap button between the two boxes reverses the pair for you, so the page becomes Rankine to Fahrenheit, where 671.67 °R gives 212 °F and 0 °R gives -459.67 °F. From the metric side the factor is 1.8: Rankine = Kelvin × 1.8, so 1 K is 1.8 °R and 373.15 K is 671.67 °R, while Rankine = (Celsius + 273.15) × 1.8 puts 0 °C at 491.67 °R and 100 °C at 671.67 °R. The To menu converts to any of those without leaving the page.

Why does this page open on Fahrenheit and Rankine when I last converted something else?

Because a page that names a pair should show that pair. This one sets Fahrenheit and Rankine on arrival, ahead of whatever the converter last remembered, and it leaves the main unit converter's own memory alone: go back to the full converter and it is still on the pair and the category you left it on. The number you last typed does travel with you, since it is usually the one you are still working on.