About the Fahrenheit to Kelvin Converter
This Fahrenheit to Kelvin converter turns a temperature in degrees Fahrenheit into kelvin, the SI unit of thermodynamic temperature, and also shows degrees Rankine and Celsius. It is built for students working physics and chemistry problems, engineers reading US-unit data sheets, and anyone who needs an absolute temperature for gas-law or radiation calculations.
Kelvin and Rankine are both absolute scales: zero means absolute zero, the point where no further thermal energy can be removed. Kelvin uses Celsius-sized steps, while Rankine uses Fahrenheit-sized steps, so Rankine is the natural absolute scale for US customary engineering work.
Enter any temperature at or above absolute zero (−459.67 °F). Values below that are physically impossible, so the converter flags them instead of producing a negative kelvin figure.
With the default inputs, the kelvin is 293.15 K. Change any value above to recalculate instantly.
How to use the fahrenheit to kelvin converter
- 1Enter the temperature in degrees Fahrenheit.
- 2Read the kelvin value as the main result.
- 3Use the Rankine figure for US engineering formulas that need an absolute temperature.
- 4Check the chart and table for common reference points.
Formula and method
A Fahrenheit degree is 5/9 the size of a kelvin, and the scales have different zero points. Subtracting 32 shifts the value to the Celsius zero (water freezing), multiplying by 5/9 rescales to Celsius-sized degrees, and adding 273.15 moves the zero to absolute zero.
Rankine keeps Fahrenheit-sized degrees but starts at absolute zero, so it is simply °F + 459.67. Because both kelvin and Rankine start at absolute zero, they differ only by the factor 1.8: K = °R ÷ 1.8. These offsets are exact by definition.
- °F
- Temperature in degrees Fahrenheit
- K
- Temperature in kelvin
- °R
- Temperature in degrees Rankine
Worked examples
Room temperature (68 °F)
68 − 32 = 36; 36 × 5/9 = 20 °C; 20 + 273.15 = 293.15 K. In Rankine it is 68 + 459.67 = 527.67 °R.
Boiling water (212 °F)
212 − 32 = 180; 180 × 5/9 = 100 °C, so water boils at 373.15 K or 671.67 °R at sea level.
Cold winter day (−40 °F)
−40 − 32 = −72; −72 × 5/9 = −40 °C (the point where both scales agree), then −40 + 273.15 = 233.15 K.
Frequently asked questions
How do you convert Fahrenheit to Kelvin?+
Subtract 32, multiply by 5/9, then add 273.15. For example, 50 °F → (50 − 32) × 5/9 = 10 °C → 283.15 K.
What is 0 Kelvin in Fahrenheit?+
0 K is absolute zero, which equals −459.67 °F and −273.15 °C. Nothing can be colder, so kelvin values are never negative.
What is the Rankine scale?+
Rankine is an absolute temperature scale that uses Fahrenheit-sized degrees. 0 °R is absolute zero, water freezes at 491.67 °R and boils at 671.67 °R.
Why is there no degree symbol on kelvin?+
Since 1967 the SI unit has been named simply "kelvin" (symbol K) because it is an absolute unit, not a degree on an arbitrary scale. Write 300 K, not 300 °K.
What is body temperature in kelvin?+
A typical body temperature of 98.6 °F equals 37 °C, which is 310.15 K.