Celsius to kelvin and kelvin to Celsius converter

Celsius to kelvin: add 273.15. Room temperature of 25 °C is 298.15 K, water boils at 100 °C = 373.15 K and absolute zero is 0 K = −273.15 °C. Enter a value and the other scale appears while you type; Fahrenheit and Rankine are shown too.

Example: Temperature 25 · Direction: Celsius to kelvin (°C → K) → Answer: 25 °C = 298.15 K. Source: BIPM – SI Brochure: kelvin and degree Celsius (t/°C = T/K − 273.15). Updated: 15 October 2026.

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Result

Answer: 25 °C = 298.15 K
Fahrenheit and Rankine: Same temperature: 77 °F and 536.67 °R (Rankine).
Working: 25 °C + 273.15 = 298.15 K
Quick check in your head: 25 + 273 ≈ 298 K (exact: 298.15 K). Adding 273 is within 0.15 K, enough for most school and lab estimates.
Conversion chart: °C K
-273.15 0
-200 73.15
-100 173.15
-40 233.15
-20 253.15
0 273.15
10 283.15
20 293.15
25 298.15
37 310.15
50 323.15
100 373.15
200 473.15
500 773.15
1,000 1,273.15
Temperatures worth knowing: Temperature °C K
Absolute zero -273.15 0
Liquid nitrogen boils (77.36 K) -195.79 77.36
Water freezes / ice melts 0 273.15
Triple point of water (273.16 K) 0.01 273.16
Room temperature 20 293.15
Body temperature 37 310.15
Water boils (at 1 atm) 100 373.15
Surface of the Sun (nominal 5,772 K) 5,498.85 5,772; Nothing can be colder than absolute zero: 0 K = −273.15 °C. A kelvin step is as large as a Celsius step, only the zero point differs.

°C	K
-273.15	0
-200	73.15
-100	173.15
-40	233.15
-20	253.15
0	273.15
10	283.15
20	293.15
25	298.15
37	310.15
50	323.15
100	373.15
200	473.15
500	773.15
1,000	1,273.15

Temperature	°C	K
Absolute zero	-273.15	0
Liquid nitrogen boils (77.36 K)	-195.79	77.36
Water freezes / ice melts	0	273.15
Triple point of water (273.16 K)	0.01	273.16
Room temperature	20	293.15
Body temperature	37	310.15
Water boils (at 1 atm)	100	373.15
Surface of the Sun (nominal 5,772 K)	5,498.85	5,772

How it is calculated

How to convert Celsius to kelvin

K = °C + 273.15. For 25 °C: 25 + 273.15 = 298.15 K. Going back, °C = K − 273.15: 373.15 K − 273.15 = 100 °C. There is no degree sign for kelvin: you write 298.15 K, not 298.15 °K. A temperature change of 1 °C is exactly 1 K, only the zero point is shifted.

Why 273.15?

The kelvin scale starts at absolute zero, the lowest possible temperature, where particles have no thermal motion to give up. That point lies at −273.15 °C. So 0 K = −273.15 °C = −459.67 °F, and the converter refuses anything colder. Water freezes at 273.15 K and boils at 373.15 K at normal pressure, 100 kelvin apart.

When you need kelvin

Gas-law and thermodynamics formulas (pV = nRT) need kelvin, because ratios of temperatures only make sense from absolute zero. Putting 20 °C into pV = nRT instead of 293.15 K gives a result that is wrong by a factor of nearly 15. Colour temperature of lamps (2,700 K warm, 6,500 K daylight) and star temperatures are also given in kelvin.

Fahrenheit and Rankine

The Rankine scale is Fahrenheit counted from absolute zero: °R = K × 1.8. So 25 °C = 298.15 K = 77 °F = 536.67 °R. For everyday Celsius and Fahrenheit use the Celsius to Fahrenheit converter.

A quick mental trick

Add 273 for kelvin, subtract 273 for Celsius: 37 °C ≈ 310 K (exact: 310.15 K). The error of 0.15 K is irrelevant outside precise lab work.

All temperature scales are on the Fahrenheit to Celsius page.

Frequently asked questions

How do you convert Celsius to kelvin?

Add 273.15 to the Celsius value. Example: 20 °C + 273.15 = 293.15 K.

How do you convert kelvin to Celsius?

Subtract 273.15 from the kelvin value. Example: 300 K − 273.15 = 26.85 °C.

What is 0 K in Celsius?

0 K is absolute zero, −273.15 °C or −459.67 °F. Nothing can be colder.

What is 37 °C in kelvin?

Body temperature of 37 °C is 310.15 K (98.6 °F).

Is it Kelvin or degrees Kelvin?

Just kelvin, written K without a degree sign (298.15 K). The degree sign belongs to Celsius, Fahrenheit and Rankine.

Sources and legal basis

As of: 15 October 2026 · Editorial policy