Fahrenheit and Kelvin are units used to measure temperature. The first is used for surface temperatures in the United States, while the second is often used in scientific equations and calculations. It is possible to convert temperatures from Fahrenheit to Kelvin and vice versa. There are two ways to perform the conversion; although both are simple, the second will provide more information as it also gives the result of the conversion to Celsius.
Method 1 of 3: Converting directly to Kelvin
Step 1. Learn the formula
There are two ways to convert from Fahrenheit to Kelvin. In the first method, just perform a simple calculation, which makes the direct conversion. The formula is: K = (y °F + 459, 67) x 5/9 (Replace “y” with the value in Fahrenheit).
If you want to convert 75°F to Kelvin, the formula is K = (75°F + 459, 67) x 5/9
Step 2. Add 459, 67 to the original temperature
On the Fahrenheit scale, absolute zero is -459.67°F, which is equivalent to 0K. Since the Kelvin scale has no negative numbers, you must first add 459.67 to any number in Fahrenheit to make it Kelvin.
In the same example (75°F conversion), the answer to the first calculation (75°F + 459, 67) is 534, 67
Step 3. Multiply the sum by 5/9 to get the temperature in Kelvin
Remember that 5/9 is 0, 55 and 5 is the repeating decimal. The answer is temperature in Kelvin.
- In the same 75°F conversion example, the second calculation answer (5/9 x 534, 67) is 297, 0388, and 8 is the repeating decimal number.
- The answer to the account (75°F + 459.67) x 5/9 is 297.0388.
- Therefore, 75°F equals 297.0388K.
Method 2 of 3: Conversion to Celsius and then Kelvin
Step 1. Learn the formulas
The second way to convert Fahrenheit to Kelvin involves calculating the temperature in Celsius first, which can be useful if you need to compare all the results. They are: formula 1 is K = (y °F – 32) x 5/9 + 273, 15 and formula 2 is K = (y °F - 32) ÷ 1.8 + 273, 15. Both produce the same result.
- If you need to transform 90°F to Kelvin, for example, formula 1 would look like this: K = (90°F - 32) x 5/9 + 273, 15.
- Formula 2 would have the following configuration: K = (90 °F - 32) ÷ 1.8 + 273, 15.
Step 2. Subtract 32 from the original temperature
Regardless of the formula used, the first step in performing the conversion from Fahrenheit to Celsius and then to Kelvin is to subtract 32 from the original temperature in Fahrenheit.
At 90°F conversion, for example, the response to the first calculation (90°F - 32) is 58
Step 3. Multiply the difference by 5/9 in formula 1
Remember that 5/9 is 0.55. The answer to the product is the temperature in Celsius.
The answer to the second calculation (58 x 0.5555) of the 90°F conversion example using formula 1 is 32.22°C, with the 2 representing the repeating decimal
Step 4. Divide the difference by 1, 8 in formula 2
Doing division by 1, 8 will have the same result as multiplying by 5/9. The quotient is the temperature in Celsius.
Again using 90°F as the basis for the conversion, the answer to the second calculation (58 ÷ 1, 8) of formula 2 is 32.22°C, with the 2 representing the repeating decimal
Step 5. Add 273, 15 to the product or quotient to get the temperature in Kelvin
The final step of the conversion is to add 273, 15 to the product of formula 1 or to the quotient of formula 2, obtaining the temperature in Kelvin. Absolute zero is equivalent to -273, 15 °C and 0 K; as the Kelvin scale has no negative numbers, you will need to add 273, 15 to the final result.
- Taking the 90°F conversion as an example, the answer to the third calculation (32, 22°C + 273, 15) is 305.37.
- the answer of (90°F - 32) x 5/9 + 273, 15 and (90°F - 32) ÷ 1.8 + 273, 15 is 305, 3722, with 2 being the repeating decimal.
- Therefore, 90°F equals 32.22°C and 305.3722K
Method 3 of 3: Converting Kelvin to Fahrenheit
Step 1. Know the formula
To convert Kelvin to Fahrenheit, just use the same formula, but in reverse. It will look like this: F = y K x 9/5 - 459.67. Replace “y” with the temperature in Kelvin you want to convert.
To convert 320 K, for example, the equation F = 320 K x 9/5 - 459, 67 is used
Step 2. Multiply the original temperature by 9/5
Remember that 9/5 can also be represented by 1, 8.
Using 320K, the first calculation (320K x 9/5) results in 576 as the product
Step 3. Subtract 459, 67 from the result to get the temperature in Fahrenheit
Once the Kelvin value is multiplied by 9/5, just subtract the result from 459.67, which is the temperature of absolute zero in Fahrenheit.
- The answer of the second calculation (576 - 459, 67) is 116.33.
- 320 K x 9/5 – 459.67 is equal to 116.33.
- Therefore, 320K is equal to 116.33°F.