Convert Fahrenheit to Kelvin
Convert degrees fahrenheit to kelvins instantly. K = (°F + 459.67) × 5/9 — use the live calculator, the exact formula, a reference-temperature table and worked examples. Also check the Kelvin to Fahrenheit converter for the reverse conversion.
Units explained
Fahrenheit
The degree Fahrenheit (°F) sets the freezing point of water at 32 °F and the boiling point at 212 °F, dividing the interval into 180 equal degrees. One degree Fahrenheit is exactly 5/9 the size of a kelvin, and °F = °C × 9/5 + 32 exactly.
Created by German-born physicist Daniel Gabriel Fahrenheit, inventor of the reliable mercury-in-glass thermometer. His zero point was the temperature of an ice-and-salt brine mixture, and his original upper fixed point sat near human body temperature.
The official everyday scale of the United States and a handful of other countries. In India, clinical thermometers and fever readings are still very commonly quoted in Fahrenheit (a '102-degree fever'), which keeps °F to °C conversion a daily need.
Introduced by Daniel Gabriel Fahrenheit in 1724 in Amsterdam, building directly on Ole Rømer's earlier scale, which Fahrenheit had studied during a 1708 visit to Copenhagen.
Kelvin
The kelvin (K) is the SI base unit of thermodynamic temperature, defined by fixing the Boltzmann constant k at exactly 1.380649×10⁻²³ J/K. Zero kelvin is absolute zero, the lowest temperature physically possible, and kelvin values are written without a degree sign.
Named for William Thomson, 1st Baron Kelvin, who in 1848 calculated the value of absolute zero (about −273 °C) and proposed an absolute thermodynamic scale. His title comes from the River Kelvin, which flows past the University of Glasgow in Scotland.
The universal temperature unit of science and engineering — physics, chemistry, astronomy, and materials science — and the standard for color temperature in photography, displays, and lighting (a 5600 K daylight bulb).
Proposed by William Thomson (Lord Kelvin) in 1848; adopted as an SI base unit by the 10th CGPM in 1954 and redefined through the fixed Boltzmann constant by the 26th CGPM, effective May 20, 2019.
Fahrenheit to Kelvin conversion formula
The exact relationship between degrees fahrenheit and kelvins:
To convert degrees fahrenheit to kelvins, add 459.67 to the value, then multiply by 5/9. To reverse, multiply the value by 9/5, then subtract 459.67.
Reference anchors: water freezes at 32 °F = 273.15 K and boils at 212 °F = 373.15 K (at standard atmospheric pressure).
How to use this converter
Type a value into the calculator. The result in kelvins updates as you type. Tap a quick value, copy the result with one click, or use the swap arrow to jump straight to the Kelvin to Fahrenheit converter for the reverse direction.
Step-by-step: convert degrees fahrenheit to kelvins
- Write down the temperature in degrees fahrenheit (°F).
- Add 459.67 to the value, then multiply by 5/9.
- The result is the same temperature expressed in kelvins (K).
- To reverse, multiply the value by 9/5, then subtract 459.67 — or open the Kelvin to Fahrenheit converter.
Worked examples
Example 1 — Convert 98.6 °F to K (human body temperature):
(98.6 + 459.67) × 5/9 = 310.15 K
Example 2 — Convert 212 °F to K (the boiling point of water):
(212 + 459.67) × 5/9 = 373.15 K
Fahrenheit to Kelvin conversion table
Physically meaningful reference temperatures, from absolute zero to the surface of the Sun, converted from degrees fahrenheit to kelvins:
| Fahrenheit [°F] | Kelvin [K] | Reference point |
|---|---|---|
| -459.67 | 0 | Absolute zero |
| -40 | 233.15 | Where Celsius and Fahrenheit coincide (−40°) |
| 0 | 255.3722222222 | Zero Fahrenheit (0 °F) |
| 32 | 273.15 | Water freezes (0 °C / 32 °F) |
| 32.018 | 273.16 | Triple point of water |
| 50 | 283.15 | Cool day (10 °C / 50 °F) |
| 68 | 293.15 | Room temperature (20 °C / 68 °F) |
| 77 | 298.15 | Standard laboratory temperature (25 °C) |
| 86 | 303.15 | Hot day (30 °C / 86 °F) |
| 98.6 | 310.15 | Human body temperature (37 °C / 98.6 °F) |
| 104 | 313.15 | Heat-wave day (40 °C / 104 °F) |
| 122 | 323.15 | Hot tap water (50 °C / 122 °F) |
| 212 | 373.15 | Water boils (100 °C / 212 °F) |
| 356 | 453.15 | Moderate baking oven (180 °C / 356 °F) |
| 9940.73 | 5778 | Surface of the Sun (≈5,505 °C) |
Frequently asked questions
What is 98.6 °F in K?
How do I convert degrees fahrenheit to kelvins?
How do I convert kelvins back to degrees fahrenheit?
At what temperature do the Fahrenheit and Kelvin scales read the same number?
Can a temperature be below absolute zero?
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Sources & references
Conversion relationship (K = (°F + 459.67) × 5/9) verified against the following authoritative sources:
- BIPM — The International System of Units (SI Brochure 9th ed.)
Official BIPM publication defining the seven SI base units (including the meter) and the rules for their use. The global authority on units of measurement.
- NIST — Guide to the SI
US National Institute of Standards and Technology reference covering the SI base and derived units with definitions and usage rules for US technical practice.
- NIST Special Publication 811 — Guide for the Use of the International System of Units
Detailed NIST guide covering exact conversion factors between SI and US customary units along with formatting and rounding conventions.
- BIPM — International Temperature Scale of 1990 (ITS-90)
The internationally agreed practical temperature scale, defining fixed points (including the triple point of water at 273.16 K) and interpolation instruments used by national metrology institutes for thermometer calibration worldwide.
- CODATA Internationally Recommended Values of the Fundamental Physical Constants
Committee on Data of the International Science Council; authoritative source for the masses of fundamental particles (electron, proton, neutron) and the atomic mass constant.