Kelvin to Celsius Converter
ConversionsChoose kelvin to Celsius or Celsius to kelvin and enter a temperature. You get the converted value and the same temperature in degrees Fahrenheit, with a chart of common temperatures and the steps.
Step by step
293.15 − 273.15 = 20
- Degrees Celsius = kelvin − 273.15: 293.15 − 273.15 = 20 °C.
- For comparison, degrees Fahrenheit = degrees Celsius × 9/5 + 32: 20 × 9/5 + 32 = 68 °F.
Once every entry is valid, you’ll see each step of the calculation here.
Formula
- K
- temperature in kelvin, the thermodynamic temperature T
- °C
- temperature in degrees Celsius, the Celsius temperature t
- °F
- temperature in degrees Fahrenheit
How it works
The kelvin (K) is the SI unit of temperature. Its scale starts at absolute zero, the lowest temperature possible, so there are no negative kelvins. The degree Celsius (°C) is the scale of everyday weather in most of the world and of the science lab. The two units are the same size: a change of 1 °C is exactly a change of 1 K. Only the zero point differs. The SI Brochure defines the Celsius temperature as the difference from a reference temperature of 273.15 K, which is close to the ice point.
So the conversion is a single addition or subtraction: K = °C + 273.15 and °C = K − 273.15. A room at 20 °C is 293.15 K, 0 °C is 273.15 K and 100 °C is 373.15 K. Absolute zero is 0 K, which is −273.15 °C, and the converter does not go below it. In a chemistry class you may round 273.15 to 273. That is fine for a rough answer, but it makes the result 0.15 too low when converting to kelvin.
The converter also shows the temperature in degrees Fahrenheit, the scale used for US weather and cooking: °F = °C × 9/5 + 32. To start from Fahrenheit, change it to Celsius first with the Fahrenheit to Celsius converter, then add 273.15, or use K = (°F − 32) × 5/9 + 273.15 in one go. The chart under the converter lists the kelvin values of common temperatures, from absolute zero and dry ice to body temperature and the boiling point of water.
The formula
The number 273.15 is fixed by definition: the Celsius temperature is the difference t = T − T₀, with T₀ = 273.15 K. Until 2019 the kelvin was defined by setting the triple point of water to exactly 273.16 K. Since 2019 it is defined by fixing the Boltzmann constant at k = 1.380649 × 10⁻²³ J/K. Neither change affects the conversion, which stays 273.15 apart.
For a temperature difference you do not add 273.15. A difference has the same number in kelvins and in degrees Celsius, so a room that warms by 5 °C warms by 5 K. That is why units such as thermal conductivity are written with K, as in W/(m·K).
Example
A lab protocol calls for a water bath at 25 °C. What is that in kelvin?
- Kelvin = degrees Celsius + 273.15: 25 + 273.15 = 298.15 K.
- In degrees Fahrenheit: 25 × 9/5 + 32 = 77 °F.
- Thermodynamic data tables are often given at 298.15 K, which is exactly 25 °C. For comparison, 20 °C is 293.15 K and 100 °C is 373.15 K.
25 °C equals 298.15 K, which is 77 °F.
Load this example into the calculatorFrequently asked questions
How do you convert Kelvin to Celsius? What is the equation?
Subtract 273.15 from the kelvin value: °C = K − 273.15. So 300 K is 26.85 °C, 373.15 K is 100 °C and 0 K is −273.15 °C. Choose "K → °C" in the converter and type the kelvins. The result appears as you type, with Fahrenheit next to it.
Do you add 273 to Celsius to get Kelvin?
Yes, but the exact number is 273.15. Adding 273 gives a good rough answer, and 273.15 gives the exact one: 20 °C is 293.15 K, or about 293 K. Use 273.15 whenever the decimals matter, for example in lab work and homework that asks for two decimals.
How do I convert C to K in chemistry?
Add 273.15 to the temperature in degrees Celsius: K = °C + 273.15. Gas law problems such as PV = nRT need kelvin, so convert first. For 25 °C, the result is 298.15 K. Many courses allow 273, so follow what your instructor asks for.
Why do scientists use Kelvin instead of Celsius?
Kelvin is an absolute scale: its zero is absolute zero, the lowest temperature possible, and the temperature is proportional to the average kinetic energy of the random motion of the particles. Formulas such as the ideal gas law only work with absolute temperatures. Kelvin is also the SI unit of temperature, so it is the one used in published data.
What are -95 degrees Celsius, 245 degrees Celsius and -146 degrees Celsius in kelvin?
Add 273.15 to each value, and keep the sign for the negative ones. -95 degrees Celsius is 178.15 K, 245 degrees Celsius is 518.15 K and -146 degrees Celsius is 127.15 K. Convert negative temperatures the same way: -95 + 273.15 = 178.15.
How do you convert 87 Kelvin to degrees Celsius?
Subtract 273.15: 87 K is 87 − 273.15 = −186.15 °C. Any value below 273.15 K gives a negative Celsius temperature, and 0 K is the lowest possible at −273.15 °C. In degrees Fahrenheit, 87 K is −303.07 °F.
What are 0 °C, 1 °C, 20 °C and 30 °C in kelvin?
0 °C is 273.15 K, 1 °C is 274.15 K, 20 °C is 293.15 K and 30 °C is 303.15 K. Body temperature, 37 °C, is 310.15 K. To go the other way, 0 K is −273.15 °C, and the chart under the converter lists more.
How do I convert Fahrenheit to Kelvin?
Subtract 32, multiply by 5/9 and add 273.15: K = (°F − 32) × 5/9 + 273.15. For 68 °F, that is 36 × 5/9 + 273.15 = 20 + 273.15 = 293.15 K. This converter takes Celsius or kelvin as input, so for Fahrenheit, change to Celsius first with the Fahrenheit to Celsius converter.
What is Celsius (°C) used for?
Celsius is the everyday temperature scale in most of the world and the standard in science classes, where 0 °C is near the freezing point of water and 100 °C near its boiling point at sea level. The US uses Fahrenheit for weather and cooking but Celsius in science.
Why does temperature conversion use +32 or +459.67?
The 32 is where the Fahrenheit scale puts the freezing point of water: 0 °C is 32 °F. The 459.67 moves the Fahrenheit zero to absolute zero, which is −459.67 °F, giving the Rankine scale: °R = °F + 459.67. Kelvin does the same for Celsius with 273.15.
Is Centigrade the same as Celsius?
Yes. Centigrade was the older name for the same scale, with 100 steps between the freezing and boiling points of water. In 1948 the General Conference on Weights and Measures adopted the name degree Celsius, so scientific writing now uses Celsius.
Which unit is absolute: Celsius, Fahrenheit, Kelvin or Rankine?
Kelvin and Rankine are absolute scales, because both start at absolute zero. Celsius and Fahrenheit are relative scales with zeros chosen by convention, which is why they have negative values. A kelvin is the same size as a degree Celsius, and a Rankine degree is the same size as a degree Fahrenheit.
Why is it K and not °K?
Because in 1967 the General Conference on Weights and Measures settled the name: the unit is the kelvin, symbol K, and no longer the "degree Kelvin" with the symbol °K. Write 300 K, not 300 °K. The degree sign stays with °C and °F.
Do these conversions depend on pressure, like the boiling point of water?
No. Converting between Celsius and kelvin is a fixed offset of 273.15 and does not depend on pressure or on the substance. What does depend on pressure is the temperature at which water boils. At sea level it is about 100 °C, or 373.15 K, and it is lower at altitude.
- The International System of Units (SI Brochure, 9th edition): the kelvin and the Celsius temperature, t/°C = T/K − 273.15 (BIPM, International Bureau of Weights and Measures)
- Kelvin (Wikipedia)
- Celsius (Wikipedia)
- Absolute zero (Wikipedia)
- Thermodynamic temperature (kinetic energy of particle motion and absolute zero) (Wikipedia)