Convert Temperature from Kelvin to Celsius and Back

Kelvin and Celsius are two temperature scales. The size of the "degree" for each scale is the same magnitude, but the Kelvin scale starts at absolute zero (the lowest temperature theoretically attainable), while the Celsius scale sets its zero point at the triple point of water (the point at which water can exist in solid, liquid, or gaseous states, or 32.01 F).

Converting between the Kelvin and the Celsius requires only basic arithmetic.

Conversion Formula

The formula to convert Kelvin into Celsius is C = K - 273.15. All that is needed to convert Kelvin to Celsius is one simple step:

Take your Kelvin temperature and subtract 273.15. Your answer will be in Celsius. The K does not use the word degree or the symbol; depending on the context, generally one or the other (or simply C) is used to report a Celsius temperature.

Kelvin to Celsius

How many degrees Celsius is 500 K?

C = 500 - 273.15
500 K = 226.85 C

Let's convert normal body temperature from Kelvin to Celsius. Human body temperature is 310.15 K. Put the value into the equation to solve for degrees Celsius:

C = K - 273.15
C = 310.15 - 273.15
Human body temperature = 37 C

Reverse Conversion: Celsius to Kelvin

Similarly, it's easy to convert a Celsius temperature to the Kelvin scale. You can either use the formula given above or use K = C + 273.15.

For example, let's convert the boiling point of water to Kelvin. The boiling point of water is 100 C. Plug the value into the formula:

K = 100 + 273.15
K = 373.15

About Absolute Zero

While typical temperatures experienced in daily life are often expressed in Celsius or Fahrenheit, many phenomena are described more easily using an absolute temperature scale. The Kelvin scale starts at absolute zero (the coldest temperature attainable) and is based on energy measurement (the movement of molecules). The Kelvin is the international standard for scientific temperature measurement, and is used in many fields, including astronomy and physics.

While it's perfectly normal to get negative values for Celsius temperature, the Kelvin scale only goes down to zero. Zero K is also known as absolute zero. It is the point at which no further heat can be removed from a system because there is no molecular movement, so there is no lower temperature possible.

Similarly, this means the lowest possible Celsius temperature you can ever get is minus 273.15 C. If you ever perform a temperature calculation that gives you a value lower than that, it's time to go back and check your work.