Celsius
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Celsius to Kelvin Calculator
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Formula: K = °C + 273.15
Converted K
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KOffset +273.15
Offset
+273.15
Kelvin
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Type
Absolute
How this Celsius to Kelvin calculator works
Enter a temperature in degrees Celsius. The calculator adds 273.15 and shows the result in kelvin. The formula is K = °C + 273.15.
Celsius and kelvin use steps of the same size. A rise of 1°C is a rise of 1 K. What changes is the zero. Celsius sets 0 at the freezing point of water. Kelvin sets 0 at absolute zero, which is −273.15°C. That is why every Celsius reading shifts upward by 273.15.
Worked example: 37°C is normal body temperature. 37 + 273.15 = 310.15, so the page shows 310.15 K. The result is rounded to at most six decimal places. Any finite number is accepted, including temperatures below zero.
The four cards under the converter repeat the inputs of that sum: the Celsius value you typed, the fixed offset of +273.15, the Kelvin result, and the scale type, Absolute. The circle beside the result is only a picture of the input. It starts empty at −50°C and fills completely at 100°C. A temperature outside that window still converts with the same addition.
Celsius to Kelvin examples
Each Kelvin value is the Celsius value plus 273.15, using the same rounding as the calculator.
| Celsius (°C) | Kelvin (K) | What it marks |
|---|---|---|
| −273.15 | 0 | Absolute zero |
| −40 | 233.15 | Very cold |
| −10 | 263.15 | Below freezing |
| 0 | 273.15 | Water freezes |
| 20 | 293.15 | Mild room |
| 25 | 298.15 | Typical room |
| 37 | 310.15 | Body temperature |
| 100 | 373.15 | Water boils |
How to read the result
Add 273.15
There is no multiply step. 20°C becomes 293.15 K because 20 + 273.15 = 293.15.
Same degree size
A 10 degree rise on the Celsius input is a 10 kelvin rise in the result.
Absolute zero
−273.15°C converts to 0 K. That is the lowest point on the kelvin scale.
Symbol K
The result is written as a number and K, such as 373.15 K for boiling water.
Frequently asked questions
How do you convert Celsius to Kelvin?
Add 273.15 to the Celsius temperature. K = °C + 273.15. A comfortable room at 25°C is 25 + 273.15 = 298.15 K. The size of one degree is the same on both scales, so only the starting point changes.
What is 0°C in Kelvin?
0 + 273.15 = 273.15 K. That is the freezing point of water at standard atmospheric pressure. Kelvin does not place zero at the freezing point of water.
What is the boiling point of water in Kelvin?
Water boils at 100°C under standard atmospheric pressure. 100 + 273.15 = 373.15 K.
What is absolute zero on this calculator?
Absolute zero is 0 K, which is −273.15°C. Entering −273.15 returns 0 K. A temperature one degree warmer, −272.15°C, returns 1 K.
Why is the offset 273.15 and not 273?
The modern definition fixes 0°C at 273.15 K. Adding 273 would be 0.15 K too low. This calculator always adds 273.15, so 0°C is 273.15 K and 20°C is 293.15 K.
Is a change of 1°C the same as a change of 1 K?
Yes. Both scales use the same interval. If a liquid warms from 20°C to 30°C, that is a rise of 10°C and also a rise of 10 K, from 293.15 K to 303.15 K.
Can the result be below 0 K?
The formula will still add 273.15 to any number you enter. −273.16°C returns −0.01 K. A negative Kelvin value is below absolute zero and is not a physical temperature. The calculator does not block it.
How do I turn a Kelvin result back into Celsius?
Subtract 273.15. °C = K − 273.15. A result of 310.15 K is 310.15 − 273.15 = 37°C, which is normal human body temperature.
Why is Kelvin written as K, without a degree sign?
Kelvin is an absolute temperature scale. This page shows the result as a number followed by K, for example 298.15 K. The Celsius input is still labelled °C.
Why does the circle fill between −50°C and 100°C?
The ring is a visual scale. It is empty at −50°C and full at 100°C. The Kelvin number is not limited by that ring. 200°C still converts to 473.15 K.