Celsius to Kelvin Converter

Convert Celsius to kelvin instantly, with a reference table covering absolute zero, everyday temperatures and lab conditions.

Degrees Celsius

Kelvins

1 °C = 274.15 K

Multiply degrees Celsius by 1, then add 273.15, to get kelvins.

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Degrees Celsius to kelvins reference table

The conversions people look up most often, rounded to 2 decimal places.

Common degrees Celsius to kelvins conversions
Degree Celsius (°C)	Kelvin (K)
-273.15 °C	0 K
-200 °C	73.15 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
200 °C	473.15 K
500 °C	773.15 K
1,000 °C	1,273.15 K

The degrees Celsius people look up most

-273.15 °C = 0 K: Absolute zero, exactly 0 K. Nothing can be colder, which is why the scale starts here rather than at a freezing point.
0 °C = 273.15 K: Water freezes, 273.15 K. The offset is exact by definition, and a Kelvin degree is the same size as a Celsius one.
20 °C = 293.15 K: Room temperature, 293.15 K. Laboratory standard conditions are usually quoted here or at 25 degrees.
25 °C = 298.15 K: The reference temperature behind most published chemistry and physics constants, and the standard state for thermodynamic data.
37 °C = 310.15 K: Body temperature, 310.15 K. Kelvin is rarely used for anything biological, but the conversion still gets asked.
100 °C = 373.15 K: Water boils at sea level, 373.15 K - one atmosphere of pressure assumed, as always with boiling points.

How the celsius to kelvin calculation works

Kelvin and Celsius use the same size degree, so the conversion is addition alone:

K = °C + 273.15

That shared step size is deliberate. The kelvin was defined so that a one-degree change means the same thing on both scales; only the zero point differs. Which means a temperature difference of 10°C is a difference of 10 K exactly — no conversion needed.

Kelvin has no degree symbol and no "degrees". It is written 300 K, not 300°K, and read as "300 kelvin". Celsius and Fahrenheit take the degree sign because they are relative scales; kelvin is absolute.

Zero kelvin is absolute zero — −273.15°C — the point at which a system has no thermal energy left to remove. It is unreachable in principle, not merely in practice: the third law of thermodynamics rules it out in any finite number of steps. Laboratories have reached within a few billionths of a kelvin.

Reference points:

0 K → −273.15°C — absolute zero
77 K → −196.15°C — liquid nitrogen, the everyday laboratory cold
273.15 K → 0°C — water freezes
293.15 K → 20°C — "room temperature" in most physics problems
310.15 K → 37°C — body temperature
373.15 K → 100°C — water boils at sea level

Why it matters outside a lab: the gas laws, thermal radiation, and anything involving a ratio of temperatures only work in absolute units. Doubling the pressure of a gas at constant volume doubles its kelvin temperature — a calculation that is meaningless in Celsius, where the zero is arbitrary.

To convert back, subtract 273.15.

Frequently asked questions

Why is the offset 273.15 and not simply 273?

Because it was pinned to the triple point of water rather than to its freezing point. From 1954 to 2019 the kelvin was defined by putting the triple point at exactly 273.16 K, and freezing at ordinary pressure sits 0.01 K below that - hence 273.15. The kelvin is now defined through the Boltzmann constant, and 273.15 is fixed by the definition of the Celsius scale itself.

Is 25°C the standard temperature for chemistry data?

It depends which standard is meant, and the two are often confused. IUPAC standard temperature and pressure is 0°C, or 273.15 K, at 100 kPa, while most thermodynamic tables are published at 25°C, or 298.15 K. A gas volume quoted at STP and an enthalpy quoted at standard conditions therefore use different temperatures - a difference of about 9% in a gas volume calculation.

Does water still boil at exactly 100°C?

Not exactly, though the difference only shows in a calibration laboratory. Celsius was originally set with water boiling at 100 degrees, but once the temperature scale was pinned to other fixed points the measured boiling point at one atmosphere came out at 99.974°C, or 373.124 K. Altitude matters far more: the boiling point falls roughly 1°C for every 300 m of elevation.

Celsius to Kelvin Converter