Fahrenheit to kelvin and kelvin to Fahrenheit converter
Fahrenheit to kelvin: K = (°F + 459.67) × 5/9, so 68 °F = 293.15 K. Type °F and the kelvin value follows as you type, with °C and Rankine underneath; kelvin to Fahrenheit works in the same box.
Example: Temperature 68 · Direction: Fahrenheit to kelvin (°F → K) → Answer: 68 °F = 293.15 K. Source: NIST SP 811, Appendix B.8 – kelvin, degree Fahrenheit and degree Rankine: t/°F = 1.8 (T/K) − 459.67. Updated: .
How it is calculated
The formula
K = (°F + 459.67) × 5 ÷ 9, and the reverse °F = K × 9 ÷ 5 − 459.67. Absolute zero (0 K) is -459.67 °F, so you add that offset first and then scale by 5/9, because a kelvin is 1.8 times larger than a degree Fahrenheit. Examples: 32 °F = 273.15 K (freezing water), 212 °F = 373.15 K (boiling at sea level) and, back again, 300 K = 80.33 °F.
Where engineers need it
The ideal gas law, radiation and thermodynamic tables need absolute temperatures. US data sheets often list room conditions in °F: 77 °F is 298.15 K, the usual reference temperature of chemistry tables (25 °C). 68 °F is 293.15 K. Body temperature of 98.6 °F is 310.15 K, and an oven at 350 °F is 449.82 K. The line under the answer also gives Rankine, the absolute scale that uses Fahrenheit-sized degrees: 68 °F is 527.67 °R.
Differences need no offset
A temperature difference converts with the factor alone: a rise of 18 °F is a rise of 10 K, because 1 °F = 5/9 K. Only absolute readings need the 459.67 offset. Mixing these up is the usual error in heat-transfer homework: the heat capacity in J/(kg·K) per kelvin equals J/(kg·°C), and per °F it is smaller by 5/9.
Cold values
At -40 °F the Fahrenheit and Celsius scales meet, and that is 233.15 K. At absolute zero, -459.67 °F, the converter returns exactly 0 K, and anything colder produces an error message instead of a number. Liquid nitrogen boils at 77.36 K, which is -320.42 °F.
Quick estimate
Add 460, divide by 1.8: 100 °F is about 311.1 K (exact: 310.93). The shortcut is about 0.18 K high. For Celsius see celsius to kelvin and Fahrenheit to Celsius.
Frequently asked questions
What is the formula for Fahrenheit to kelvin?
K = (°F + 459.67) × 5/9. For 68 °F: (68 + 459.67) × 5/9 = 293.15, so 68 °F = 293.15 K.
What is 0 °F in kelvin?
0 °F = 255.37 K.
How do I convert kelvin to Fahrenheit?
°F = K × 9/5 − 459.67. Example: 300 K = 80.33 °F.
Is room temperature of 72 °F about 295 K?
Yes: 72 °F = 295.37 K.
What is the lowest Fahrenheit temperature?
Absolute zero, -459.67 °F, which is 0 K. The converter does not accept values below it.
Sources and legal basis
- NIST SP 811, Appendix B.8 – kelvin, degree Fahrenheit and degree Rankine: t/°F = 1.8 (T/K) − 459.67
- BIPM – The International System of Units (SI Brochure, 9th edition)
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