How do you convert Celsius to kelvin?
Add 273.15. No multiplication is involved: a difference of 1 °C equals exactly 1 K. The kelvin simply counts from absolute zero instead of the freezing point of water.
°C = K − 273.15
Reference temperatures in Celsius and kelvin
| −273.15 °C (absolute zero) | 0 K |
| −40 °C | 233.15 K |
| 0 °C (ice) | 273.15 K |
| 20 °C (room temp.) | 293.15 K |
| 37 °C (human body) | 310.15 K |
| 100 °C (boiling) | 373.15 K |
| 1,000 °C | 1,273.15 K |
| 5,505 °C (surface of the Sun) | 5,778 K |
Show every value
- 1 °C = 1 K
- 2 °C = 2 K
- 3 °C = 3 K
- 4 °C = 4 K
- 5 °C = 5 K
- 6 °C = 6 K
- 7 °C = 7 K
- 8 °C = 8 K
- 9 °C = 9 K
- 10 °C = 10 K
- 11 °C = 11 K
- 12 °C = 12 K
- 13 °C = 13 K
- 14 °C = 14 K
- 15 °C = 15 K
- 16 °C = 16 K
- 17 °C = 17 K
- 18 °C = 18 K
- 19 °C = 19 K
- 20 °C = 20 K
- 21 °C = 21 K
- 22 °C = 22 K
- 23 °C = 23 K
- 24 °C = 24 K
- 25 °C = 25 K
- 26 °C = 26 K
- 27 °C = 27 K
- 28 °C = 28 K
- 29 °C = 29 K
- 30 °C = 30 K
- 31 °C = 31 K
- 32 °C = 32 K
- 33 °C = 33 K
- 34 °C = 34 K
- 35 °C = 35 K
- 36 °C = 36 K
- 37 °C = 37 K
- 38 °C = 38 K
- 39 °C = 39 K
- 40 °C = 40 K
- 41 °C = 41 K
- 42 °C = 42 K
- 43 °C = 43 K
- 44 °C = 44 K
- 45 °C = 45 K
- 46 °C = 46 K
- 47 °C = 47 K
- 48 °C = 48 K
- 49 °C = 49 K
- 50 °C = 50 K
- 51 °C = 51 K
- 52 °C = 52 K
- 53 °C = 53 K
- 54 °C = 54 K
- 55 °C = 55 K
- 56 °C = 56 K
- 57 °C = 57 K
- 58 °C = 58 K
- 59 °C = 59 K
- 60 °C = 60 K
- 61 °C = 61 K
- 62 °C = 62 K
- 63 °C = 63 K
- 64 °C = 64 K
- 65 °C = 65 K
- 66 °C = 66 K
- 67 °C = 67 K
- 68 °C = 68 K
- 69 °C = 69 K
- 70 °C = 70 K
- 71 °C = 71 K
- 72 °C = 72 K
- 73 °C = 73 K
- 74 °C = 74 K
- 75 °C = 75 K
- 76 °C = 76 K
- 77 °C = 77 K
- 78 °C = 78 K
- 79 °C = 79 K
- 80 °C = 80 K
- 81 °C = 81 K
- 82 °C = 82 K
- 83 °C = 83 K
- 84 °C = 84 K
- 85 °C = 85 K
- 86 °C = 86 K
- 87 °C = 87 K
- 88 °C = 88 K
- 89 °C = 89 K
- 90 °C = 90 K
- 91 °C = 91 K
- 92 °C = 92 K
- 93 °C = 93 K
- 94 °C = 94 K
- 95 °C = 95 K
- 96 °C = 96 K
- 97 °C = 97 K
- 98 °C = 98 K
- 99 °C = 99 K
- 100 °C = 100 K
- 125 °C = 125 K
- 150 °C = 150 K
- 175 °C = 175 K
- 200 °C = 200 K
- 225 °C = 225 K
- 250 °C = 250 K
- 275 °C = 275 K
- 300 °C = 300 K
- 325 °C = 325 K
- 350 °C = 350 K
- 375 °C = 375 K
- 400 °C = 400 K
- 425 °C = 425 K
- 450 °C = 450 K
- 475 °C = 475 K
- 500 °C = 500 K
- 550 °C = 550 K
- 600 °C = 600 K
- 650 °C = 650 K
- 700 °C = 700 K
- 750 °C = 750 K
- 800 °C = 800 K
- 850 °C = 850 K
- 900 °C = 900 K
- 950 °C = 950 K
- 1,000 °C = 1,000 K
- 1,500 °C = 1,500 K
- 2,000 °C = 2,000 K
- 2,500 °C = 2,500 K
- 3,000 °C = 3,000 K
- 3,500 °C = 3,500 K
- 4,000 °C = 4,000 K
- 4,500 °C = 4,500 K
- 5,000 °C = 5,000 K
- 5,500 °C = 5,500 K
- 6,000 °C = 6,000 K
- 6,500 °C = 6,500 K
- 7,000 °C = 7,000 K
- 7,500 °C = 7,500 K
- 8,000 °C = 8,000 K
- 8,500 °C = 8,500 K
- 9,000 °C = 9,000 K
- 9,500 °C = 9,500 K
- 10,000 °C = 10,000 K
Since the 2019 SI revision, the kelvin is defined by fixing the Boltzmann constant at 1.380 649 × 10⁻²³ J/K. The 273.15 offset between the two scales remains exact by definition. Methodology & sources.
Frequently asked questions
Why does kelvin have no degree symbol?
Because it is not a degree but the unit of an absolute scale starting at absolute zero. You write 300 K, not 300 °K: the degree sign was dropped from the notation in 1967.
Can absolute zero be reached?
No. The third law of thermodynamics forbids reaching it in a finite number of steps. Laboratories get down to a few billionths of a kelvin, but never to zero.
When should I work in kelvin rather than Celsius?
Whenever a formula involves a ratio of temperatures: the ideal gas law, radiation, thermodynamic efficiency. Dividing 40 °C by 20 °C carries no physical meaning; dividing 313.15 K by 293.15 K does.
Should a temperature difference be written in Celsius or in kelvin?
Both are allowed, since a difference of 1 °C equals 1 K, but derived units only ever use the kelvin: thermal conductivity in W/(m·K), the specific heat of water at 4,186 J/(kg·K), a resistor's temperature coefficient in ppm/K. The trap is adding 273.15: a 20 °C difference stays 20 K, never 293.15 K.
Where does the number 273.15 come from?
From water. Between 1954 and 2019 the kelvin was defined as 1/273.16 of the temperature of the triple point of water, fixed by convention at 273.16 K, that is 0.01 °C. Celsius zero therefore sat exactly 0.01 K below, at 273.15 K. Since 2019 the kelvin rests on the Boltzmann constant and the triple point is a measured value again, uncertain by about a tenth of a millikelvin, while the 273.15 gap between the two scales stays exact.