Celsius to Kelvin Converter
Convert °C to K by adding 273.15, with reference points
K = °C + 273.15. To convert Celsius to kelvin, add 273.15 to the Celsius temperature. For example, 0 °C = 273.15 K and 25 °C = 298.15 K.
How to convert Celsius to kelvin
A kelvin and a degree Celsius are exactly the same size. The only difference is where zero sits. Celsius puts zero near the freezing point of water, while the kelvin scale starts at absolute zero, the coldest temperature possible, which is −273.15 °C. So converting is a single shift: add 273.15. There is no multiplying, unlike the Celsius to Fahrenheit conversion, and the full temperature converter shows the same reading in Rankine and Réaumur too.
Since the 2019 redefinition of the SI, the kelvin is fixed by the Boltzmann constant, exactly 1.380649 × 10−23 J/K, and the degree Celsius is defined as the kelvin minus 273.15. The 273.15 is therefore exact by definition. Using 273 instead is common in school problems but introduces a 0.15 K error. The kelvin is written without a degree sign (300 K, not 300 °K), and because nothing is colder than absolute zero, a kelvin temperature can never be negative. Gas-law problems pair kelvin with absolute pressure, often in kilopascals; the psi to kPa converter handles US pressure readings, but add atmospheric pressure to a gauge value first.
Step by step
- Take the temperature in degrees Celsius.
- Add 273.15.
- Write the result in kelvin, with no degree sign: 298.15 K, not 298.15 °K.
- For a temperature difference, add nothing: a change of 1 °C is a change of 1 K.
See it on a scale
Worked examples
Liquid nitrogen at about −196 °C, a standard laboratory temperature of 25 °C, and water boiling at 100 °C.
K = -196 + 273.15 = 77.15
= 77.15 K
K = 25 + 273.15 = 298.15
= 298.15 K
K = 100 + 273.15 = 373.15
= 373.15 K
Is kelvin the same as Celsius?
No, but a kelvin and a degree Celsius are exactly the same size; the scales differ only in where zero sits, so a temperature in kelvin is always 273.15 higher than the same temperature in Celsius.
That shared size is by design. The SI Brochure defines the degree Celsius as equal in magnitude to the kelvin, so an interval of 1 °C is the same as 1 K, and a kettle that warms water by 30 °C has warmed it by 30 K.
The difference is the zero. Celsius zero sits at 273.15 K, close to the freezing point of water, while the kelvin scale starts at absolute zero. That makes Celsius a relative scale that goes negative every winter and kelvin an absolute scale that never can.
| Situation | Celsius | Kelvin |
|---|---|---|
| A reading: a winter night | −10 °C | 263.15 K |
| A reading: a warm afternoon | 30 °C | 303.15 K |
| A change: a 12-degree daily swing | 12 °C | 12 K |
How is the kelvin defined today?
Since 20 May 2019 the kelvin has been defined by fixing the Boltzmann constant at exactly 1.380649 × 10−23 J/K, which ties temperature directly to energy instead of to a property of water.
Before that, the kelvin was 1/273.16 of the thermodynamic temperature of the triple point of water, the single condition where ice, liquid water and water vapor coexist. That older definition is why the triple point sits at exactly 0.01 °C: 273.16 K minus the 273.15 offset. Today the triple point is a measured value, still 273.16 K within a tiny uncertainty. The joule in the constant is the SI unit of energy, covered by the energy converter.
Laboratories do not measure the Boltzmann constant every time. They calibrate thermometers to the International Temperature Scale of 1990 (ITS-90), which assigns exact temperatures to reproducible fixed points and names the instruments, such as platinum resistance thermometers, that interpolate between them.
| ITS-90 fixed point | Kelvin | Celsius |
|---|---|---|
| Triple point of mercury | 234.3156 K | −38.8344 °C |
| Triple point of water | 273.16 K | 0.01 °C |
| Melting point of gallium | 302.9146 K | 29.7646 °C |
| Freezing point of tin | 505.078 K | 231.928 °C |
| Freezing point of zinc | 692.677 K | 419.527 °C |
How do I convert Celsius to kelvin in Excel or Google Sheets?
Enter =A2+273.15 beside a Celsius value in A2, or use =CONVERT(A2,"C","K"); for 25 °C both return 298.15.
One formula copied down a column handles a whole run of lab readings. Go the other way with =A2-273.15 or =CONVERT(A2,"K","C"). In Excel the longer codes "cel" and "kel" work as well. For a column of temperature differences, such as heating rises, add nothing, because 1 °C of change is 1 K of change.
If your data is in Fahrenheit, one formula does both steps: =(A2-32)*5/9+273.15, or =CONVERT(A2,"F","K"). A reading of 212 °F returns 373.15 K. For the Fahrenheit step on its own, the Fahrenheit to Celsius converter shows the working.
Keep full precision in the cells and round only for display, for example =ROUND(A2+273.15,2), since the offset already carries two decimal places.
Celsius to kelvin conversion chart
Celsius temperatures from absolute zero to 1,000 °C, converted to kelvin. Every value is exact because the offset of 273.15 is fixed by definition.
| Celsius (°C) | Kelvin (K) |
|---|---|
| -273.15 °C | 0 K |
| -250 °C | 23.15 K |
| -200 °C | 73.15 K |
| -196 °C | 77.15 K |
| -150 °C | 123.15 K |
| -100 °C | 173.15 K |
| -80 °C | 193.15 K |
| -50 °C | 223.15 K |
| -40 °C | 233.15 K |
| -30 °C | 243.15 K |
| -20 °C | 253.15 K |
| -10 °C | 263.15 K |
| 0 °C | 273.15 K |
| 10 °C | 283.15 K |
| 15 °C | 288.15 K |
| 20 °C | 293.15 K |
| 25 °C | 298.15 K |
| 30 °C | 303.15 K |
| 37 °C | 310.15 K |
| 40 °C | 313.15 K |
| 50 °C | 323.15 K |
| 60 °C | 333.15 K |
| 70 °C | 343.15 K |
| 80 °C | 353.15 K |
| 90 °C | 363.15 K |
| 100 °C | 373.15 K |
| 150 °C | 423.15 K |
| 200 °C | 473.15 K |
| 250 °C | 523.15 K |
| 300 °C | 573.15 K |
| 400 °C | 673.15 K |
| 500 °C | 773.15 K |
| 1,000 °C | 1,273.15 K |
Celsius vs kelvin: what is the difference?
The degree Celsius and the kelvin measure temperature in steps of identical size, so the whole difference lies in their zero points and in how scientists use them.
| Attribute | Celsius | Kelvin |
|---|---|---|
| Symbol | °C | K |
| System | Metric (SI derived) | SI base unit |
| Defined as | K − 273.15 | absolute zero = 0 K |
| Water freezes at | 0 °C | 273.15 K |
| Water boils at (1 atm) | 100 °C | 373.15 K |
| Absolute zero | -273.15 °C | 0 K |
| Type of scale | Relative: zero near the freezing point of water | Absolute: zero at absolute zero |
| Negative values | Yes, below 0 °C | Never |
| How it is written | With a degree sign: 25 °C | No degree sign: 298.15 K |
| SI status | Derived unit with a special name | One of the seven SI base units |
| Typical uses | Weather, medicine, cooking and lab bench readings | Thermodynamics, gas laws, cryogenics and the color temperature of light |
4 key differences
- A temperature difference of 1 °C equals a difference of exactly 1 K, so only readings need the 273.15 offset.
- The triple point of water is 0.01 °C, or 273.16 K.
- Room temperature, about 20 °C, is 293.15 K, so everyday kelvin values sit near 300.
- Doubling an absolute temperature in kelvin doubles the pressure of an ideal gas held at fixed volume; doubling a Celsius reading does not.
Scientific reference points in Celsius and kelvin
Physical and chemical landmarks at standard atmospheric pressure where relevant. Absolute zero is exact by definition; the other values are measured and rounded to two decimals.
| Reference point | Celsius | Kelvin |
|---|---|---|
| Absolute zero | −273.15 °C | 0.00 K |
| Liquid helium boils | −268.93 °C | 4.22 K |
| Liquid nitrogen boils | −195.79 °C | 77.36 K |
| Dry ice (solid CO₂) sublimes | −78.46 °C | 194.69 K |
| Mercury freezes | −38.83 °C | 234.32 K |
| Water freezes (standard pressure) | 0.00 °C | 273.15 K |
| Triple point of water | 0.01 °C | 273.16 K |
| Room temperature | 20.00 °C | 293.15 K |
| Standard ambient temperature (SATP) | 25.00 °C | 298.15 K |
| Human body | 37.00 °C | 310.15 K |
| Water boils (sea-level pressure) | 99.97 °C | 373.12 K |
| Surface of the Sun (nominal) | 5,498.85 °C | 5,772.00 K |
What does the kelvin number on a light bulb mean?
The kelvin number on a light bulb box describes the color of the light, not how hot the bulb gets. It is the temperature an ideal glowing object would need to give off light of that color, so low numbers look orange and high numbers look bluish. The Celsius column shows what that temperature would be, which is purely for interest.
| Color temperature | Same value in °C | What it looks like |
|---|---|---|
| 1,900 K | 1,626.85 °C | Candle flame |
| 2,700 K | 2,426.85 °C | Warm white; like an incandescent bulb |
| 3,000 K | 2,726.85 °C | Soft white; halogen |
| 3,500 K | 3,226.85 °C | Neutral white |
| 4,000 K | 3,726.85 °C | Cool white; offices and kitchens |
| 5,000 K | 4,726.85 °C | Daylight bulb; photo and print viewing |
| 6,500 K | 6,226.85 °C | Overcast daylight; the D65 standard for screens |
When should you use kelvin instead of Celsius?
Use kelvin whenever a formula multiplies or divides by temperature, as in gas laws, thermal radiation and reaction rates.
For everyday readings, Celsius is easier. For physics and chemistry, kelvin is often required, because many formulas depend on temperature measured from absolute zero. The ideal gas law, PV = nRT, is the classic example: pressure and volume are proportional to temperature only when T is in kelvin.
Ratios only work in kelvin
Is 40 °C “twice as hot” as 20 °C? No. In kelvin, 20 °C is 293.15 K and 40 °C is 313.15 K, only 6.8% higher. A sealed container of gas heated from 20 °C to 40 °C would see its pressure rise by that same 6.8%, not double. Any time you divide one temperature by another, convert to kelvin first.
Differences are the same in both
A rise of 15 °C is a rise of 15 K. That is why heat-capacity values are often written per kelvin (J/kg·K) even when experiments are run in Celsius. Energy calculations that use these values, such as heating water, can be finished with the joules to calories converter.
Common mistakes with kelvin
- Writing “degrees kelvin” or °K. Since 1967 the unit has simply been the kelvin, symbol K. Say “300 kelvins” or “300 K”.
- Using 273 instead of 273.15. Fine for rough work, but exam answers and lab reports usually expect 273.15.
- Adding 273.15 to a difference. A temperature change of 10 °C is 10 K, not 283.15 K.
- Getting a negative kelvin value. That means the input was below −273.15 °C, which is physically impossible, or the sign was typed wrong.
- Capitalizing the unit name. The unit is written kelvin in lowercase, like meter and second, while the symbol is a capital K. Only the scientist, Lord Kelvin, gets a capital letter.
Who was Kelvin?
William Thomson, a Belfast-born physicist at the University of Glasgow, proposed an absolute temperature scale in 1848. He was made Baron Kelvin in 1892, taking the name from the River Kelvin that runs past the university, and the unit was later named after him. An absolute scale using Fahrenheit-sized degrees, the Rankine scale, is still found in some US engineering work.
Sources and further reading
The standards and references behind the numbers on this page. Links open in a new tab.
Standards and official sources
Further reading
- Degree CelsiusWikipedia
- KelvinWikipedia
Celsius to kelvin FAQs
Short, exact answers to what people ask most.
How do you convert Celsius to kelvin?
Add 273.15 to the Celsius temperature: K = °C + 273.15. For example, 20 °C + 273.15 = 293.15 K.
What is 0 °C in kelvin?
0 °C is exactly 273.15 K. The freezing point of water at standard pressure is very close to this value.
Why is it 273.15 and not 273?
Because the degree Celsius is defined as the kelvin minus exactly 273.15, which places absolute zero at −273.15 °C. Using 273 is a rounding that leaves a 0.15 K error.
Can kelvin be negative?
No. Zero kelvin is absolute zero, the lowest possible temperature, so kelvin readings are always zero or positive. A negative result means the Celsius input was below −273.15 °C or was entered incorrectly.
Why is there no degree symbol in kelvin?
The kelvin is an SI base unit in its own right, not a degree on a scale, and the General Conference on Weights and Measures dropped “degree Kelvin” in 1967. It is written 300 K, not 300 °K.
What is room temperature in kelvin?
Room temperature is usually taken as 20 to 25 °C, which is 293.15 to 298.15 K. Chemists often use 25 °C, or 298.15 K, as standard ambient temperature.
What is 100 °C in kelvin?
100 °C is 373.15 K. Water boils close to this at standard sea-level pressure; on ITS-90 the value is about 99.97 °C.
What is 37 °C in kelvin?
37 °C, the classic figure for normal human body temperature, is 310.15 K.
What is −196 °C in kelvin?
−196 °C is 77.15 K, just below the boiling point of liquid nitrogen at 77.36 K (−195.79 °C).
What is 50 °C in kelvin?
50 °C is 323.15 K. Every 50 °C step adds exactly 50 K, so 150 °C is 423.15 K.
What is 1,000 °C in kelvin?
1,000 °C is 1,273.15 K. At furnace temperatures the 273.15 offset is a small share of the total, about 21%.
Related conversions
The kelvin and the degree Celsius per the BIPM SI Brochure (9th ed., 2019) and the 13th CGPM (1967); fixed points from the International Temperature Scale of 1990 (ITS-90); boiling and sublimation points from the NIST Chemistry WebBook; nominal solar effective temperature of 5,772 K from IAU Resolution B3 (2015); spreadsheet syntax from the Microsoft Excel and Google Sheets CONVERT function documentation. Last updated . How we verify our numbers.