Converting Fahrenheit to Kelvin

Worked Temperature Unit Conversion Example

Bundled up man in a snowstorm holding up a thermometer


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This example problem illustrates the method to convert Fahrenheit to Kelvin. Fahrenheit and Kelvin are two important temperature scales. The Fahrenheit scale is used primarily in the United States, while the Kelvin scale is used in some areas of science. Aside from homework questions, the most common times you might need to convert between Kelvin and Fahrenheit would be working with equipment using the different scales or when trying to plug a Fahrenheit value into a Kelvin-based formula.

The zero point of the Kelvin scale is absolute zero, which is the point at which it's not possible to remove any additional heat. The zero point of the Fahrenheit scale is the lowest temperature Daniel Fahrenheit could attain in his lab (using a mixture of ice, salt, and water). Because the zero point of the Fahrenheit scale and degree size are both somewhat arbitrary, the Kelvin to Fahrenheit conversion requires a tiny bit of math. For many people, it's easier to first convert Fahrenheit to Celsius and then Celsius to Kelvin because these formulas are often memorized. Here's an example:

Fahrenheit To Kelvin Conversion Problem

A healthy person has a body temperature of 98.6 °F. What is this temperature in Kelvin?

First, convert Fahrenheit to Celsius. The formula to convert Fahrenheit to Celsius is
TC = 5/9(TF - 32)

Where TC is temperature in Celsius and TF is temperature in Fahrenheit.
TC = 5/9(98.6 - 32)
TC = 5/9(66.6)
TC = 37 °C
Next, convert °C to K:
The formula to convert °C to K is:
TK = TC + 273
TK = TC + 273.15

Which formula you use depends on how many significant figures you are working with in the conversion problem. It's more accurate to say the difference between Kelvin and Celsius is 273.15, but most of the time, just using 273 is good enough.
TK = 37 + 273
TK = 310 K

The temperature in Kelvin of a healthy person is 310 K.

Fahrenheit To Kelvin Conversion Formula

Of course, there is a formula you can use to convert directly from Fahrenheit to Kelvin:

K = 5/9 (° F - 32) + 273

where K is temperature in Kelvin and F is temperature in degrees Fahrenheit.

If you plug in body temperature in Fahrenheit, you can solve the conversion to Kelvin directly:

K = 5/9 (98.6 - 32) + 273
K = 5/9 (66.6) + 273
K = 37 + 273
K = 310

The other version of the Fahrenheit to Kelvin conversion formula is:

K = (°F – 32) ÷ 1.8 + 273.15

Here, dividing (Fahrenheit - 32) by 1.8 is the same as if you multiplied it by 5/9. You should use whichever formula makes you more comfortable, as they give the same result.

No Degree in the Kelvin Scale

When you are converting or reporting a temperature in the Kelvin scale, it's important to remember this scale does not have a degree. You do use degrees in Celsius and Fahrenheit. The reason there's no degree in Kelvin is because it's an absolute temperature scale.

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Your Citation
Helmenstine, Anne Marie, Ph.D. "Converting Fahrenheit to Kelvin." ThoughtCo, Apr. 5, 2023, Helmenstine, Anne Marie, Ph.D. (2023, April 5). Converting Fahrenheit to Kelvin. Retrieved from Helmenstine, Anne Marie, Ph.D. "Converting Fahrenheit to Kelvin." ThoughtCo. (accessed May 30, 2023).