How it works
Enter a temperature, pick the unit it’s in, and pick the unit you want. The answer is shown in that unit, with the same temperature in the third unit below it.
Every conversion goes through Celsius. A Fahrenheit temperature is turned into Celsius first, then into the unit you asked for. Kelvin is the easiest: it’s Celsius with 273.15 added.
The formula
| From | To | Formula |
|---|---|---|
| Celsius | Fahrenheit | °F = °C × 1.8 + 32 |
| Fahrenheit | Celsius | °C = (°F − 32) ÷ 1.8 |
| Celsius | Kelvin | K = °C + 273.15 |
| Kelvin | Celsius | °C = K − 273.15 |
| Fahrenheit | Kelvin | K = (°F − 32) ÷ 1.8 + 273.15 |
| Kelvin | Fahrenheit | °F = (K − 273.15) × 1.8 + 32 |
- °C is degrees Celsius, °F is degrees Fahrenheit, and K is kelvins.
- 1.8 is the size of a Celsius degree in Fahrenheit degrees. Water freezes at 0 °C and boils at 100 °C, a gap of 100 Celsius degrees. In Fahrenheit that’s 32 °F to 212 °F, a gap of 180 degrees, and 180 ÷ 100 = 1.8. (You’ll often see it written as 9/5, which is the same number.)
- 32 is where water freezes on the Fahrenheit scale, so the two scales start 32 apart.
- 273.15 is how far 0 °C is above absolute zero, where the Kelvin scale starts.
Worked example
Want this with your own numbers? See Show the work above.
Room temperature is often taken as 25 °C. What is that in Fahrenheit and in kelvins?
- Write the formula: °F = 25 × 1.8 + 32.
- Multiply: 25 × 1.8 = 45.
- Add 32: 45 + 32 = 77 °F.
For kelvins, add 273.15: 25 + 273.15 = 298.15 K.
Going back the other way, 77 °F − 32 = 45, and 45 ÷ 1.8 = 25 °C, where you started.
FAQ
Is there a quick way to convert in my head?
For Celsius to Fahrenheit, double the number and add 30. For Fahrenheit to Celsius, take away 30 and halve it. This is close (within 2 degrees) between 0 °C and 20 °C, which covers most weather, but it drifts further off the hotter or colder it gets. At 30 °C it gives 90 °F instead of 86 °F.
At what temperature are Celsius and Fahrenheit the same?
At −40. −40 °C is exactly −40 °F: −40 × 1.8 + 32 = −72 + 32 = −40. It’s the only temperature where the two scales meet.
What is absolute zero?
The coldest temperature possible: 0 K, which is −273.15 °C or −459.67 °F. Nothing can be colder, so the converter asks for a temperature at or above it.
Why is Kelvin written without a degree sign?
Kelvin is an absolute scale that starts at absolute zero, and in the SI the kelvin is a unit in its own right, like the meter. So you write 300 K (“300 kelvins”), not 300 °K. Celsius and Fahrenheit keep the degree sign.
How do I convert a change in temperature?
A change, or difference, only needs the size of the degrees, not the starting point. Multiply a change in Celsius by 1.8 to get the change in Fahrenheit, without adding 32. So a rise of 10 °C is a rise of 18 °F. A change of 1 °C is the same size as a change of 1 K. This converter is for temperatures, not changes.
Sources
- Conversion formulas for Celsius, Fahrenheit, and kelvin: NIST Guide to the SI (SP 811), Appendix B.9, Temperature
- Conversion equations, room temperature example, and fixed points: OpenStax College Physics 2e, section 13.1, Temperature
Cite this page
APA (7th edition)
Mathlark. (2026, September 30). Temperature converter. https://mathlark.com/conversions/temperature-converter/
MLA (9th edition)
"Temperature Converter." Mathlark, 30 Sept. 2026, mathlark.com/conversions/temperature-converter/.