Convert K to °F kelvins ↔ degrees Fahrenheit Free Online Secure
Type a temperature in kelvins and read it in degrees Fahrenheit at once. The relation is exact by definition, the arithmetic happens in your browser, and nothing is sent anywhere.
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Common values — Convert K to °F (kelvins ↔ degrees Fahrenheit)
| K | °F |
|---|---|
| 0 | -459.67 |
| 100 | -279.67 |
| 200 | -99.67 |
| 273.15 | 32 |
| 293.15 | 68 |
| 310.15 | 98.6 |
| 373.15 | 212 |
| 500 | 440.33 |
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.
Is it true that −40 °C and −40 °F are the same?
Yes, and it is the only place the two scales meet. Fahrenheit degrees are smaller than Celsius ones — nine of them to every five — and the two scales start from different zeros; the one temperature where the difference in size and the difference in starting point cancel out exactly is minus forty. Below that, the Fahrenheit number is the lower of the two.
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.
Light bulbs, cameras and screens: kelvin into Fahrenheit
The box of an LED bulb says 2700 K, a camera menu offers 5600 K for flash and a display setting offers 6500 K. These numbers are colour temperatures, given in kelvin, and a reader used to Fahrenheit may wonder how hot such a light really is. To convert K to °F, multiply by 9/5 and subtract 459.67: 2700 K is 4,400.3 °F, 5600 K is 9,620.3 °F and 6500 K is 11,240.3 °F. The calculator above does both steps as you type, and the sections below explain what the numbers mean for lighting, photography, film, screens and the natural world.
You will find the formula with worked examples, a short profile of each scale, a comparison, a long set of practical cases and the slips to avoid. The arithmetic runs in your browser, and what you type is not sent anywhere.
How to convert K to °F: multiply by 9/5 and subtract 459.67
The formula
The formula is °F = K × 9/5 − 459.67, or equivalently °F = (K − 273.15) × 9/5 + 32. So 300 K gives 300 × 1.8 − 459.67 = 80.33 °F, 373.15 K gives 212 °F and 0 K gives −459.67 °F. To go back, add 459.67 and multiply by 5/9.
Worked examples
A candle flame at 1850 K is 2,870.3 °F. A warm white bulb at 2700 K is 4,400.3 °F. Daylight at 5600 K is 9,620.3 °F. The surface of the Sun at 5772 K is 9,929.9 °F, and an overcast sky at 7500 K is 13,040.3 °F.
Why two steps
A kelvin is 1.8 times larger than a Fahrenheit degree, so you multiply by 1.8. The scales also start at different places: absolute zero is −459.67 °F, so you take that offset away.
A quick sanity test
At 255.37 K the result must be 0 °F, and at 233.15 K it must be −40 °F. If a method does not pass those two checks, a step is wrong.
The kelvin
The scale of colour temperature
The kelvin is the SI unit of temperature. In lighting it measures colour temperature, the temperature of an ideal glowing black body whose colour matches the light. It is written K, with no degree sign.
Where it appears
Light bulb packaging, camera menus, display settings and film data sheets.
The Fahrenheit scale
The American scale
Fahrenheit puts 32 at the freezing point of water and 212 at the boiling point. It is the everyday scale in the United States, where lighting packaging uses kelvin for colour but where most readers think of heat in Fahrenheit.
Where it appears
American weather, kitchens, thermostats and household products.
Kelvin against Fahrenheit
One kelvin equals 1.8 degrees Fahrenheit. A shift in colour of 1000 K on a camera is a shift of 1800 °F in the equivalent black-body temperature. The absolute values are far apart: 5600 K is 9,620 °F, so the numbers do not resemble each other, but the kelvin value is the one that photographers and lighting designers use.
The formula is exact, so rounding appears only when you display the result. The key point is that a colour temperature is not the temperature of the lamp itself.
Where the conversion shows up
Light bulbs
Lighting packaging in the US lists warm white at 2700 K, which is 4,400 °F, soft white at 3000 K, or 4,940 °F, bright white at 3500 to 4100 K, or 5,840 to 6,920 °F, and daylight at 5000 to 6500 K, or 8,540 to 11,240 °F. The standard nominal values are 2700, 3000, 3500, 4000, 5000 and 6500 K. A “convert K to °F” calculation shows how far these figures are from the temperature of the glass bulb, which is only a few hundred degrees.
Photography and film
Tungsten film and video lights are balanced for 3200 K, which is 5,300 °F, and daylight film and flash for 5600 K, or 9,620 °F. Camera presets list tungsten near 3200 K, fluorescent near 4000 K, daylight at 5200 to 5600 K, cloudy at 6000 to 7000 K and shade at 7500 K, which is 13,040 °F.
Screens
Most displays use a white point of 6500 K, standard D65, which is 11,240 °F. Older televisions often defaulted to 9300 K, or 16,280 °F, which looks bluish. Night-shift modes move toward 2700 to 3400 K, or 4,400 to 5,700 °F, to reduce blue light in the evening.
Candlelight and fire
A candle flame has a colour temperature near 1850 K, or 2,870 °F, and a campfire is about 1500 to 1800 K, which is 2,240 to 2,780 °F. Dimmed incandescent bulbs shift toward 2000 K, or 3,140 °F, and many LED lamps imitate the effect with a "dim to warm" function. The warmth we find cosy is simply a low colour temperature.
Grow lights
Plants respond to the spectrum of light, and growers use lamps near 6500 K, or 11,240 °F, for leafy growth and 2700 to 3000 K, or 4,400 to 4,940 °F, for flowering. Full-spectrum LED fixtures are advertised at 4000 to 5000 K, which is 6,740 to 8,540 °F. The number is a convenience, as the spectrum matters more.
Sports lighting
Stadium lights are set to 5000 to 5700 K, which is 8,540 to 9,800 °F, to give good colour for broadcasts. Broadcast cameras are white-balanced to the venue lighting, so crews run a “convert K to °F” calculation when they compare notes with colleagues in other countries. A mismatch makes the grass look off. Stadium engineers use kelvin, and a US venue manager reading the spec can use the Fahrenheit equivalent to relate it to everyday life.
Stars and the Sun
The Sun is 5772 K, which is 9,930 °F, while red giants are 3500 K, or 5,840 °F, and blue stars exceed 10,000 K, or 17,540 °F. Colour temperature and true temperature coincide for stars, since they are near-perfect black bodies. A photograph of the night sky with a 4000 K white balance will tint the stars and the sky differently.
Wien's law
The peak wavelength of black-body radiation is 2898 micrometre-kelvins divided by the temperature. At 2700 K, which is 4,400 °F, the peak is at 1,073 nanometres, in the infrared, so an incandescent bulb gives most of its energy as heat. At 5772 K the peak is at 502 nanometres, in green light. This is why LEDs, which make light directly, are more efficient.
Lamp surface temperature versus colour temperature
An incandescent filament runs near 2700 to 3000 K, or 4,400 to 4,940 °F, matching its colour temperature. An LED bulb with a 2700 K rating has a case near 140 to 175 °F, or 333 to 353 K, because the colour temperature has nothing to do with the heat. Never read a colour temperature as a safety limit.
Spreadsheet formulas
Put kelvin values in column A and use =A2*9/5-459.67 in column B. For the reverse, use =(B2+459.67)*5/9. For mired, use =1000000/A2. Format with one decimal for temperatures and none for mired. Label each column so that a reader does not confuse colour temperature with a physical measurement.
Rounding and precision
Colour temperatures are nominal: a lamp sold as 2700 K may be anywhere between 2580 and 2870 K. Converting to 4,400.3 °F adds false precision. Quote 4,400 °F, or simply "about 4,400", and keep the label as the manufacturer's tolerance allows.
A mental shortcut
Multiply by 1.8 and take away 460. For 3000 K: 5400 minus 460 gives 4940 °F, close to the exact 4,940.3. For 6500 K: 11,700 minus 460 gives 11,240 °F. The shortcut is accurate to a fraction of a degree at these high temperatures, and it keeps the arithmetic in your head.
Landmarks to memorise
2700 K is 4,400 °F, 3200 K is 5,300 °F, 5000 K is 8,540 °F, 5600 K is 9,620 °F and 6500 K is 11,240 °F. These five cover most lighting questions. Add 255.37 K for 0 °F and 273.15 K for 32 °F for everyday temperatures.
Reference ladder
0 K is −459.67 °F. 77 K is −321.1 °F. 255.37 K is 0 °F. 273.15 K is 32 °F. 373.15 K is 212 °F. 1000 K is 1,340.3 °F. 1850 K is 2,870.3 °F. 2700 K is 4,400.3 °F. 6500 K is 11,240.3 °F. A ladder like this makes a quick check easy.
Sunrise, noon and overcast skies
Direct sunlight at noon is about 5500 K, which is 9,440 °F. Near sunrise or sunset the light drops to 2000 to 3500 K, or 3,140 to 5,840 °F. An overcast sky is 6500 to 7500 K, or 11,240 to 13,040 °F, and open shade under a blue sky can reach 8000 K, or 13,940 °F. Photographers quote all these in kelvin.
Checking by reversing
To check any convert K to °F result, add 459.67 and multiply by 5/9. If 2700 K became 4,400.3 °F, then 4,400.3 plus 459.67 is 4,859.97 and times 5/9 gives 2,700. A second test is the size: at these temperatures the Fahrenheit figure is almost twice the kelvin figure.
Temperature differences
A change of 1000 K on a colour dial is a change of 1800 °F in the black-body equivalent, but the lamp itself does not warm by that amount. For real temperature differences, such as a boiler heating water by 50 K, the equivalent is 90 °F. Do not subtract 459.67 from a difference.
Writing the unit properly
Write kelvin as K without a degree sign: 2700 K, not 2700 °K. Write Fahrenheit as °F with the sign: 4,400 °F. On packaging a figure like "2700K" without a space is common, but SI style leaves a space. Mixed units in a spec sheet should be labelled clearly.
Smart bulbs and apps
Smart-bulb apps let you choose a colour temperature from 2200 to 6500 K, which is 3,500 to 11,240 °F. They often name presets: relax, reading, concentrate and energise. The same app may show kelvin in one menu and a slider labelled warm to cool in another. A quick convert K to °F helps match a preset with a physical bulb in a spec sheet.
Reading the Lighting Facts label
American packaging includes a Lighting Facts panel with brightness in lumens, energy cost, life, light appearance in kelvin and whether the lamp contains mercury. A bulb labelled 3000 K is 4,940 °F in black-body terms. The panel gives only the kelvin number, since the Fahrenheit equivalent is a curiosity, not a product feature.
Welding arcs and furnaces
A welding arc glows far hotter than any lamp, with plasma near 6000 to 10,000 K, which is 10,340 to 17,540 °F. Glass blowers watch the colour of molten glass at around 1400 K, or 2,060 °F, shifting from orange to yellow as it heats. Technicians once estimated temperature from colour alone, and a “convert K to °F” calculation converts these readings to the units of an American manual.
Infrared cameras
A thermal camera measures infrared radiation and converts it to temperature in kelvin internally, then shows it in the chosen unit. A person at 310.15 K shows as 98.6 °F. The accuracy depends on emissivity, which is about 0.98 for skin but low for shiny metals. Set the unit once, and then check a known object, such as a cup of ice water at 273 K, which should read about 32 °F.
Moonlight
Moonlight is often given a colour temperature near 4100 K, which is 6,920 °F, although it is reflected sunlight. It looks bluish to the eye in the dark because human colour vision shifts at low light levels. Film makers imitate moonlight with lights set at 4000 to 5600 K and a blue tint, and a “convert K to °F” calculation gives the equivalent black-body temperature.
Mired and colour filters
Photographers also use mired, defined as one million divided by the temperature in kelvin. 2700 K is 370 mired, and 5600 K is 178.6 mired. A filter shifts the mired value by a fixed amount, regardless of where you start, which is why they use it for correction. A “convert K to °F” calculation tells you how hot the equivalent black body would be.
Studio and stage lighting
Fresnel lights with tungsten lamps are 3200 K, equal to 5,300 °F, while HMI and many LED panels are 5600 K, or 9,620 °F. Bi-colour LED panels let operators move between 2700 and 6500 K, which is 4,400 to 11,240 °F. A gaffer calls out a number in kelvin, and a director from the US may say "about ten thousand degrees", which is roughly right for 5600 K.
Street lighting
Old high-pressure sodium lamps were near 2000 K, or 3,140 °F, and gave a deep orange light. Modern LED street lights range from 2200 to 5000 K. Health and astronomy groups recommend 3000 K, which is 4,940 °F, or lower, to reduce blue light and sky glow. Cities now specify the kelvin number in procurement documents, and a “convert K to °F” calculation shows residents what it means in their terms.
Operating rooms and hospitals
Surgical lights are usually set to 4000 to 5000 K, which is 6,740 to 8,540 °F, for accurate colour of tissue. Waiting rooms use warmer light at 3000 to 3500 K, or 4,940 to 5,840 °F. Hospital engineers choose the figures according to standards, and a “convert K to °F” calculation helps American buyers read European data sheets.
Retail and food lighting
Shops light bread and meat with warm 2700 to 3000 K, or 4,400 to 4,940 °F, to make them look appetising. Jewellery counters use 4000 K or cooler white, which is 6,740 °F, to show diamonds. Supermarkets often tune their lighting by department. A lighting designer talks in kelvin, and a facilities manager in the US can read a Fahrenheit equivalent after a “convert K to °F” calculation.
Aquariums and reefs
Freshwater planted tanks use lamps at 6500 K, or 11,240 °F, to support plant growth. Marine reef tanks use 10,000 to 20,000 K, which is 17,540 to 35,540 °F, to show off coral fluorescence. These are bluish, high colour temperatures, and the water in the tank is only at 77 °F, or 298 K.
More values for convert K to °F
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 = -951.34 °F
- -100 K = -639.67 °F
- -20 K = -495.67 °F
- 10 K = -441.67 °F
- 15 K = -432.67 °F
- 25 K = -414.67 °F
- 30 K = -405.67 °F
- 50 K = -369.67 °F
Common slips when you convert K to °F
Forgetting the 459.67
Multiplying by 1.8 alone gives a figure about 460 degrees too high. 300 K is 80 °F, not 540 °F.
Reading colour temperature as heat
A bulb rated 6500 K is not 11,240 °F hot. The number describes the colour of the light.
Writing °K
The kelvin takes no degree sign. Write 2700 K.
Short answers
How do I convert K to °F?
Multiply by 1.8 and subtract 459.67.
What is 300 K in Fahrenheit?
80.33 °F.
What is 373.15 K in Fahrenheit?
212 °F.
What is 0 K in Fahrenheit?
−459.67 °F.
Does my number leave my device?
No, the calculation runs in your browser.
More pages and a wrap-up
For other temperature conversions see Convert K to °C, Convert K to °R, Convert °Ré to °F, Convert °R to °F, Convert °F to °R, Convert km to mi, Convert mi to km, Convert L to gal, Convert gal to L. The reverse direction is Convert °F to K.
In short, a “convert K to °F” calculation means multiplying by 1.8 and subtracting 459.67, then writing the unit beside the answer. Your number is computed locally, with no account and no upload.