Fahrenheit to Kelvin Converter
Convert °F to K when US measurements need to go into SI formulas for gas laws, radiation or chemistry.
K = (°F + 459.67) × 5/9
Two Routes From °F to K
Kelvin is the SI temperature unit, so Fahrenheit readings from US instruments, weather data or engineering specs usually need converting before they go into a physics or chemistry formula. You can get there in two ways, and they give identical answers:
Through Rankine (one step)
Adding 459.67 gives Rankine, an absolute scale with Fahrenheit-sized degrees. Multiplying by 5/9 then resizes the degrees. It's one multiplication with no intermediate rounding.
Through Celsius (two steps)
The route most people learn first. If you round the Celsius value before adding 273.15, the error carries into the kelvin result, so keep full precision in the middle step.
Fahrenheit to Kelvin Table
| °F | K | Reference |
|---|---|---|
| -459.67°F | 0 K | Absolute zero |
| -320.42°F | 77.36 K | Liquid nitrogen boils |
| -109.3°F | 194.65 K | Dry ice sublimates |
| -40°F | 233.15 K | |
| 0°F | 255.37 K | |
| 32°F | 273.15 K | Water freezes |
| 59°F | 288.15 K | Standard atmosphere, sea level |
| 68°F | 293.15 K | |
| 77°F | 298.15 K | |
| 98.6°F | 310.15 K | Body temperature |
| 212°F | 373.15 K | Water boils |
| 500°F | 533.15 K | |
| 1,000°F | 810.93 K |
Worked Example: Why Radiation Needs Kelvin
The heat a surface radiates rises with the fourth power of its absolute temperature (the Stefan–Boltzmann law). How much more does a pot of boiling water at 212°F radiate than a block of ice at 32°F, assuming the same surface?
Step 1: Convert to kelvin
Step 2: Ratio to the fourth power
The boiling pot radiates about 3.5 times as much. Using the Fahrenheit numbers directly, (212 ÷ 32)⁴, gives over 1,900 times, which is wildly wrong. Any formula with a temperature ratio or power needs an absolute scale.
Standard Reference Conditions in °F and K
"Standard conditions" isn't one fixed temperature. Different bodies define it differently, so check which one a data sheet means before converting a gas volume or density.
| Convention | °F | K | Pressure |
|---|---|---|---|
| STP (IUPAC) | 32°F | 273.15 K | 100 kPa |
| Standard atmosphere, sea level (ISA) | 59°F | 288.15 K | 101.325 kPa |
| NTP | 68°F | 293.15 K | 101.325 kPa |
| SATP | 77°F | 298.15 K | 100 kPa |
Frequently asked questions
What is 0°F in kelvin?
255.37 K. By coincidence, that is close to the effective radiating temperature of Earth, about 255 K, which is the temperature Earth would have without greenhouse warming.
Why is the result never negative?
Kelvin starts at absolute zero, −459.67°F. Anything colder is physically impossible, so this converter rejects Fahrenheit inputs below that.
How do I convert a temperature change from °F to K?
Multiply by 5/9 and ignore both offsets. A 9°F rise is a 5 K rise.
Can I skip kelvin and use Rankine instead?
Yes, if the rest of your formula is in US customary units. Rankine is also absolute, so ratios and powers come out the same. Use kelvin with SI constants.
Sources
- NIST Special Publication 811, Guide for the Use of the International System of Units (SI): Fahrenheit, Rankine and kelvin conversion factors.
Related Tools
Convert Celsius to Fahrenheit.
Convert Celsius to Kelvin.
Convert Celsius to Rankine.
Convert Fahrenheit to Celsius.
Convert Fahrenheit to Rankine.
Convert Kelvin to Celsius.