TempWise

Celsius to Kelvin Converter

Just add 273.15 — the degree size is identical, only the zero point moves.

Celsius (°C)

Kelvin (K)

Celsius → Kelvin

25 °C = 298.15 K

Type in either box — the other updates to match.

Celsius to Kelvin conversion table

−273.15 °C is absolute zero, the point where the Kelvin scale starts.

Celsius (°C)	Kelvin (K)
-273.15 °C	0 K
-100 °C	173.15 K
-40 °C	233.15 K
0 °C	273.15 K
20 °C	293.15 K
25 °C	298.15 K
37 °C	310.15 K
100 °C	373.15 K
500 °C	773.15 K
1,000 °C	1,273.15 K

What you entered

Celsius: 25 °C

1
Temperature scales have an offset, not just a ratio
25 °C → K= 298.15 K

Result

Kelvin: 298.15 K

25 °C equals 298.15 K. Temperature scales differ by an offset as well as a ratio, so there is no single multiplier.

Temperatures in Celsius and kelvin

Kelvin uses the same degree size as Celsius but starts at absolute zero, so the conversion is simply adding 273.15.

What it is	C	K
Absolute zero	-273.15	0.00
Coldest recorded on Earth	-89.2	183.95
Water freezes	0	273.15
Room temperature	20	293.15
Hot summer day	35	308.15
Body temperature	37	310.15
Water boils	100	373.15
Oven	200	473.15

Because the degree size is identical, a temperature difference is the same number in both scales - a 10 degree rise is 10 K, which is why physics formulas can use either for differences but require kelvin for absolute values. Kelvin has no degree symbol and is never written as degrees kelvin. Absolute zero at -273.15 C is the coldest possible temperature, where classical thermal motion stops entirely, and it cannot be reached even in principle.

Converting Celsius to Kelvin is the simplest temperature conversion there is: add 273.15. The two scales use degrees of exactly the same size, so no multiplication is involved at all. Only the zero point differs, and the conversion is a pure shift.

What makes Kelvin different is where that zero sits. Kelvin is an absolute scale, meaning its zero is absolute zero — the temperature at which classical thermal motion ceases and no heat can be extracted. Nothing can be colder, so Kelvin has no negative values. Celsius, by contrast, places its zero at water's freezing point, an arbitrary choice from the perspective of physics however convenient it is for daily life. Absolute zero sits at minus 273.15 degrees Celsius, which is where the offset comes from.

That absolute reference point is why science uses Kelvin. Physical laws relating temperature to other quantities generally require an absolute scale to work. The ideal gas law, for instance, says pressure is proportional to temperature — which is only true in Kelvin. Doubling the temperature of a gas from 20 to 40 degrees Celsius does not double its pressure, because in absolute terms that is a change from 293 to 313 Kelvin, a rise of under seven per cent. Using Celsius in such a calculation gives badly wrong answers, and it is a standard error in introductory physics.

One notational point: Kelvin is written without a degree symbol and without the word degree. Temperatures are '300 K', read as three hundred kelvin, not three hundred degrees Kelvin. The unit was renamed from 'degree Kelvin' in 1967 precisely to reflect its status as an absolute unit rather than a scale of degrees.

Why science needs an absolute scale

Physical laws linking temperature to other quantities require absolute temperature. The ideal gas law makes pressure proportional to temperature — true in Kelvin, false in Celsius. Heating a gas from 20 °C to 40 °C is only a rise from 293 K to 313 K, under seven per cent, not a doubling.

It's kelvin, not degrees Kelvin

Kelvin takes no degree symbol and no word 'degree' — write 300 K, read as three hundred kelvin. The unit was formally renamed from 'degree Kelvin' in 1967 to reflect that it measures absolute temperature rather than positions on a graduated scale.

Frequently asked questions

How do I convert Celsius to Kelvin?

Add 273.15. So 25 °C = 298.15 K. The degree size is identical between the two scales, so there's no multiplication — only the shift in where zero sits.

What is absolute zero?

The temperature at which classical thermal motion stops and no further heat can be extracted: 0 K, or −273.15 °C. Nothing can be colder, which is why the Kelvin scale has no negative values.

Why can't I use Celsius in gas law calculations?

Because those laws require absolute temperature. Pressure is proportional to temperature in Kelvin, not Celsius. Using Celsius makes a rise from 20° to 40° look like a doubling when in absolute terms it's a change from 293 K to 313 K — under seven per cent.

Is a kelvin the same size as a degree Celsius?

Yes, exactly. A change of one kelvin equals a change of one degree Celsius. The two scales differ only in where zero is placed, which is why the conversion is a simple addition.