Convert K to °R kelvins ↔ degrees Rankine Free Online Secure
Type a value in kelvins and read it in degrees Rankine at once. The factor is exact by definition, the arithmetic happens in your browser, and nothing is sent anywhere.
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Common values — Convert K to °R (kelvins ↔ degrees Rankine)
| K | °R |
|---|---|
| 0 | 0 |
| 100 | 180 |
| 200 | 360 |
| 273.15 | 491.67 |
| 293.15 | 527.67 |
| 310.15 | 558.27 |
| 373.15 | 671.67 |
| 500 | 900 |
Where these units come from
Fahrenheit set his zero in 1724 at the coldest thing he could make reliably — a brine of ice, water and salt — and put body heat near 96, so that his scale could be divided and divided again. Celsius published his in 1742 the other way up, with 0 for boiling and 100 for freezing; it was turned around after his death, which is why he is remembered for a scale he never used. Kelvin is the only one of the four that begins where there is nothing left to take away: absolute zero. Since 2019 it is defined by fixing the Boltzmann constant rather than by the triple point of water, so the kelvin no longer depends on a particular substance. Rankine is Fahrenheit's degree counted from absolute zero, and Réaumur, with 80 degrees between freezing and boiling, survives mostly in old recipes and in a few cheese dairies.
Where you meet them
Celsius runs weather, cooking and medicine almost everywhere; Fahrenheit does the same work in the United States and keeps a foothold in oven settings and in American recipes. Kelvin belongs to physics, to the colour temperature of lamps and screens, and to anything cold enough that negative numbers would be a nuisance. Rankine appears in American thermodynamics, and Réaumur mainly in historical texts — which is exactly why an old recipe can mislead someone reading it as Celsius.
Questions people ask
Why does the kelvin have no degree sign?
Because since 1967 it is a unit in its own right, written K and read as kelvin, not degrees Kelvin. Zero kelvin is absolute zero, which is −273.15 °C, and a step of one kelvin is exactly the same size as a step of one degree Celsius. That makes conversion a matter of adding or subtracting 273.15.
What is the Rankine scale?
An absolute scale with degrees the size of Fahrenheit degrees. Zero Rankine is absolute zero, and water freezes at 491.67 °R. To convert from kelvin you multiply by 9/5. It appears in some American engineering and thermodynamics work, where Fahrenheit-sized steps are convenient but a true zero is needed.
Is the answer exact?
Where both units are defined in terms of one another by whole numbers, yes — the page says so above the figure, and the only rounding is in how many digits are shown. Where the ratio has no finite decimal, the page shows twelve significant digits and says the relation is approximate rather than pretending otherwise.
Does anything I type leave my device?
No. The arithmetic runs in your browser; nothing is uploaded and there is no server to upload it to. Load the page once and it keeps working with the network switched off.
Spacecraft thermal design: kelvin into Rankine
A satellite is a thermal puzzle. One side faces the Sun at more than 1,300 watts per square metre, the other looks at deep space near 3 kelvin, and the electronics inside must stay within a narrow band. Teams working for American customers or from older English-unit reports often express the same numbers in degrees Rankine. To convert K to °R, multiply by 9/5: 300 K is 540 °R, 273.15 K is 491.67 °R and 40 K is 72 °R. The calculator above multiplies as you type, and the sections below show what the figures mean for sunlight, radiators, cryogenic instruments and thermal tests.
You will find the formula with worked examples, a short profile of each scale, a comparison, a long set of cases from spaceflight and the slips to avoid. The arithmetic runs in your browser, and what you type is not sent anywhere.
How to convert K to °R: multiply by 9/5
The formula
The formula is °R = K × 9/5, which is K × 1.8. So 300 K gives 540 °R, 373.15 K gives 671.67 °R and 5,772 K gives 10,389.6 °R. To go back, divide by 1.8. Both scales start at absolute zero, so there is no offset to add or subtract.
Worked examples
Liquid nitrogen at 77.36 K is 139.25 °R. Liquid helium at 4.2 K is 7.56 °R. Room temperature, 293.15 K, is 527.67 °R. The equilibrium temperature of a sphere at Earth's distance from the Sun, about 278.6 K, is 501.5 °R.
Why only a multiplication
Kelvin and Rankine both start at absolute zero. They differ only in the size of the degree: one kelvin is 1.8 Rankine degrees, so a single multiplication does the conversion.
A quick sanity test
The Rankine value is always exactly 80 per cent larger than the kelvin value. If a “convert K to °R” calculation result is not 1.8 times the input, the factor was wrong.
The kelvin
The scale of space science
The kelvin is the SI unit of temperature, used by space agencies worldwide in thermal models, test plans and instrument specifications. It is written K, without a degree sign.
Where it appears
Thermal models, instrument data sheets, test specifications and mission reports.
The Rankine scale
The English-unit absolute scale
Rankine is absolute temperature in Fahrenheit-sized degrees. It appears in older American aerospace documents and in calculations that also use feet, pounds and Btu. The symbol is °R.
Where it appears
Older NASA reports, contractor specifications in English units and thermodynamics textbooks.
Kelvin against Rankine
One kelvin equals 1.8 degrees Rankine. A temperature swing of 100 K on a satellite surface is a swing of 180 °R. Both scales are absolute, so ratios of temperatures are identical: 600 K over 300 K is 2, just as 1080 °R over 540 °R is 2.
The multiplication is exact, so no rounding appears in the conversion. The only common slip is to confuse Rankine with Fahrenheit.
Where the conversion shows up
The Sun's heat on a spacecraft
The solar constant is about 1,361 W/m², which is 431 Btu per hour per square foot. A flat plate at Earth's distance, facing the Sun, with equal absorptivity and emissivity and radiating from one side, reaches about 394 K, while a sphere averages 278.6 K, or 501.5 °R. The “convert K to °R” calculation step turns the model results into English units for a customer's report.
Radiators
A radiator at 300 K, or 540 °R, with an emissivity of 0.85 gives off 390 W/m², which is 124 Btu per hour per square foot. At 330 K, or 594 °R, it emits 572 W/m². Radiation grows with the fourth power of absolute temperature, so the choice of scale matters only for the constant.
Electronics limits
Typical electronics are qualified from −40 to +85 °C, which is 233.15 to 358.15 K, or 419.7 to 644.7 °R. Batteries prefer 273 to 313 K, or 491.7 to 563.4 °R. Hydrazine propellant freezes at about 274.7 K, which is 494.5 °R, so tanks need heaters.
The James Webb Space Telescope
Webb's mirror and optics sit near 40 K, which is 72 °R, and its mid-infrared detector is cooled to about 7 K, or 12.6 °R. The sunshield keeps the cold side near 36 K, or 64.8 °R, while the sun-facing side reaches about 383 K, or 689 °R. A difference of about 347 K, or 625 °R, spans the sunshield layers.
Batteries in orbit
A lithium-ion pack in orbit is kept between 278 and 303 K, or 500 and 545 °R, by heaters and radiators. Charging below 273 K, or 491.7 °R, risks lithium plating. A mission operator reading telemetry may see values in raw counts, converted by a table into kelvin and then into °R for an English-unit report.
Re-entry capsules
A capsule returning from the Moon meets surface temperatures of several thousand kelvin. A heat shield surface at 3,000 K is 5,400 °R, and at 2,500 K it is 4,500 °R. At those values the simple multiplication by 1.8 is all that is needed, since the offset between kelvin and Rankine is zero.
Antennas and sensors
Radio astronomy receivers are cooled to 15 to 20 K, which is 27 to 36 °R, to cut noise. Noise temperature, a measure of receiver quality, is expressed in kelvin: a system with 30 K noise temperature is 54 °R. English-unit documents sometimes give noise in °R, and a conversion keeps the figures consistent.
Spreadsheet formulas
Place kelvin values in column A and use =A2*1.8 in column B. For the reverse, use =B2/1.8. For differences, the same formula applies, since there is no offset. Label each column with its unit, and use two decimals for values near room temperature.
Rounding and precision
The multiplication is exact. Thermal models often carry three significant figures, so 278.6 K becomes 501.5 °R, not 501.480. Keep as many digits as the source supports. When a table lists both units, put the original first and the converted value in parentheses.
A mental shortcut
Double the kelvin value and subtract a tenth of the result. For 300 K: 600 minus 60 gives 540 °R. For 77 K: 154 minus 15.4 gives 138.6 °R. Because 2 minus 0.2 is exactly 1.8, the shortcut is exact.
Landmarks to memorise
4.2 K is 7.56 °R, 77 K is 138.6 °R, 273.15 K is 491.67 °R, 293.15 K is 527.67 °R, 300 K is 540 °R and 373.15 K is 671.67 °R. These six values anchor most thermal discussions in space engineering.
Reference ladder
2.725 K is 4.9 °R. 20 K is 36 °R. 100 K is 180 °R. 233.15 K is 419.67 °R. 300 K is 540 °R. 394 K is 709.2 °R. 1,000 K is 1,800 °R. 5,772 K is 10,389.6 °R. A ladder like this makes a quick check possible.
Checking by reversing
To check any convert K to °R result, divide by 1.8 and see whether you return to the start. If 300 K became 540 °R, then 540 divided by 1.8 is 300. A second test is the ratio: the Rankine figure must be 1.8 times the kelvin figure.
Relation to Fahrenheit
Rankine is Fahrenheit plus 459.67, so 540 °R is 80.33 °F. To go from kelvin to Fahrenheit, multiply by 1.8 and subtract 459.67. Space documents from American contractors usually list Fahrenheit for hot components and Rankine for equations. Moving among the three is a daily task for thermal engineers.
Cryogenic propellants
Liquid oxygen boils at 90.19 K, or 162.3 °R, and liquid hydrogen at 20.28 K, or 36.5 °R. Methane boils at 111.7 K, or 201 °R. English-unit launch documents often list propellant temperatures in °R or °F, and engineers who read them reduce both to kelvin for comparison with European data.
Temperature differences
A 10 K difference is an 18 °R difference. A 50 K swing is 90 °R. With no offset between the scales, a difference converts exactly like an absolute value. That is why thermal budgets with ΔT convert simply, while ones using Fahrenheit or Celsius need care.
Writing the units properly
Write kelvin as K, with no degree sign, and Rankine as °R with a degree sign. Put a space between number and symbol. In mixed documents label the unit on each column. A value like 540 could be a room in Rankine or a very hot object in kelvin.
Why Rankine persists in aerospace
English units persist in US aerospace because a large body of data, hardware and software was built that way, from fuel tank drawings in inches to thrust in pounds. Rankine fits as the absolute scale for such work. Newer programmes use SI and kelvin, but an engineer working across projects needs both, and a “convert K to °R” calculation formula takes seconds.
Lunar nights and survival heaters
On the Moon the night lasts about 14 Earth days, and surface temperatures fall to 100 K or below, which is 180 °R. A lander must keep batteries and electronics above their limits, around 273 K, or 491.7 °R, with radioisotope heaters or stored power. Planning the energy needed means integrating the heat loss over the temperature difference of about 173 K, or 311 °R, and the final figure is quoted in watt-hours or Btu.
Planetary probes
A probe descending to Venus meets 737 K, which is 1,327 °R, and a pressure of 92 bar. A probe to Titan meets 94 K, or 169 °R. Thermal insulation and phase-change materials extend the life of electronics for hours in such places. Reports from different space agencies list the same numbers in kelvin, Celsius or Rankine, and engineers move among them as a matter of routine.
Gravity assists and cold planets
Missions to the outer planets travel for years and pass regions where the surrounding temperature is only a few tens of kelvin. A probe near Saturn, at about 80 K in the shade, which is 144 °R, needs radioisotope heaters. The power left at the end of a mission determines how many heaters can stay on, and the thermal model is solved in kelvin, then restated in Rankine in a US contractor's report.
Testing optics at cryogenic temperatures
Telescope mirrors are tested in chambers cooled with helium to 20 K or lower, which is 36 °R. The shape of a glass or beryllium mirror changes slightly between room temperature and 40 K, and engineers measure that change with interferometers. Results are quoted per kelvin, and a test report prepared for an American agency may need the same numbers per degree Rankine, which is a factor of 1.8 smaller.
Thermal vacuum testing
Spacecraft hardware is cycled between hot and cold extremes in a vacuum chamber, often from 218 K to 398 K, which is 393 °R to 717 °R. A typical test runs four to eight cycles, with dwell times of hours at each extreme. Customers specify temperatures in their own units, and a “convert K to °R” calculation is part of reviewing the test plan, so the limits agree in every document.
Heat pipes
An ammonia heat pipe works between about 213 and 373 K, which is 383 to 672 °R. A water heat pipe works from 293 to 473 K. Heat pipes move heat with little temperature drop, often 2 or 3 K, which is 3.6 to 5.4 °R. Specifications from American suppliers may list ranges in °F, and a table of equivalents, built with a “convert K to °R” calculation on each limit, is a helpful appendix.
Earth's infrared and albedo
The Earth emits about 237 W/m² as infrared on average, 75 Btu per hour per square foot, and reflects about 30 per cent of sunlight. A satellite in low orbit receives both. Models express temperatures in kelvin, and a report for an American agency may restate them in Rankine so that heat flux and temperature share unit systems.
Multi-layer insulation
Multi-layer insulation, the gold-coloured blankets on spacecraft, can reduce radiative heat transfer by a factor of 10 to 100. Between a 300 K inside, which is 540 °R, and a 100 K outside, which is 180 °R, a blanket with an effective emittance of 0.01 passes about 4.5 W/m², compared with 45 W/m² through a bare surface of emittance 0.1. The difference is dramatic in either scale, and a “convert K to °R” calculation on each boundary temperature feeds the English-unit version of the same estimate.
Thermal expansion
Aluminium expands by about 23 parts per million per kelvin, which is 12.8 per million per degree Rankine. A 2 m structure that warms by 100 K, or 180 °R, grows by 4.6 mm. Optical benches are made of low-expansion materials so that alignment survives such changes, and the specifications are in per kelvin or per °F with the same factor of 1.8.
Heat capacity of spacecraft parts
Aluminium has a specific heat of 0.90 kJ/(kg·K), which is 0.215 Btu/(lb·°R). Heating a 100 kg aluminium panel by 10 K, or 18 °R, takes 900 kJ, which is 853 Btu. The factor between kJ/(kg·K) and Btu/(lb·°R) is 4.1868, while the factor of 1.8 applies only to the temperature change. Mixing them up is a classic error.
Solar arrays and temperature
A solar panel in orbit may range from 150 K in eclipse, 270 °R, to 380 K in sunlight, 684 °R. Silicon cells lose efficiency with heat, about 0.4 per cent per kelvin, which is 0.22 per cent per degree Rankine. At 340 K, or 612 °R, which is 40 K hotter than the reference 300 K, the loss is about 16 per cent. A “convert K to °R” calculation is used to put the datasheet in the right scale.
More values for convert K to °R
A longer list of conversions
If the value you need is not in the first list, these further conversions may be close enough to read off directly:
- -273.15 K = -491.67 °R
- -100 K = -180 °R
- -20 K = -36 °R
- 10 K = 18 °R
- 15 K = 27 °R
- 25 K = 45 °R
- 30 K = 54 °R
- 50 K = 90 °R
Common slips when you convert K to °R
Adding an offset
Kelvin and Rankine start from the same point. Do not add 459.67 or 273.15. 300 K is 540 °R.
Confusing Rankine with Fahrenheit
The degrees are the same size but the zeros differ. 540 °R is 80.33 °F, not 540 °F.
Applying 1.8 to the wrong quantity
The factor 1.8 applies to temperatures. Specific heat uses 4.1868, and heat flux 0.317, so each quantity has its own factor.
Quick questions
What is the method for a “convert K to °R” calculation?
Multiply the kelvin value by 1.8.
What is 300 K in degrees Rankine?
540 °R.
What is 273.15 K in degrees Rankine?
491.67 °R.
What is 0 K in degrees Rankine?
0 °R.
Is my figure stored or sent?
No, it stays on your device.
Where to go next
Other temperature converters are listed here: Convert K to °C, Convert K to °F, Convert °C to °R, Convert °F to °R, Convert °R to °C, Convert km to mi, Convert mi to km, Convert L to gal, Convert gal to L. If you need the opposite direction, use Convert °R to K.
The takeaway: a “convert K to °R” calculation multiplies by 1.8 and labels the result °R. The figure you enter is processed on your device only.