Temperature converters
Convert between Celsius, Fahrenheit and Kelvin for weather, cooking, science and workshop work. Pick the exact tool you need below, or use the formulas and reference charts to do it by hand.
Last updated: May 2026
Celsius, Fahrenheit and Kelvin
Three scales cover almost every temperature you will meet. Celsius and Fahrenheit are the everyday scales for weather, recipes and body temperature. Kelvin is the scientific scale, starting at absolute zero with no negative values. These converters give an instant result and handle decimals, so a reading like 36.6°C or 98.6°F converts cleanly.
Conversion formulas
Every temperature conversion is one short calculation. The Celsius to Fahrenheit step uses the ratio 9/5 (which is 1.8); the Celsius to Kelvin step is a simple offset of 273.15 because a one degree change is the same size on both scales.
| Conversion | Formula | Worked example |
|---|---|---|
| Celsius to Fahrenheit | °F = (°C × 9/5) + 32 | 20°C = 68°F |
| Fahrenheit to Celsius | °C = (°F − 32) × 5/9 | 98.6°F = 37°C |
| Celsius to Kelvin | K = °C + 273.15 | 25°C = 298.15 K |
| Kelvin to Celsius | °C = K − 273.15 | 300 K = 26.85°C |
One useful constant: Celsius and Fahrenheit meet at exactly −40°, so −40°C and −40°F are the same temperature. For a rough mental estimate from Celsius to Fahrenheit, double the number and add 30: 20°C gives about 70°F (the exact value is 68°F), which is close enough for a weather check.
Everyday temperature reference
A quick comparison of temperatures you actually deal with, shown in all three scales. Handy for sanity checking a converted value or reading an unfamiliar forecast.
| Reference point | °C | °F | K |
|---|---|---|---|
| Absolute zero | −273.15 | −459.67 | 0 |
| Water freezes | 0 | 32 | 273.15 |
| Fridge (typical) | 4 | 39 | 277 |
| Cool room | 18 | 64 | 291 |
| Room temperature | 21 | 70 | 294 |
| Warm summer day | 30 | 86 | 303 |
| Body temperature | 37 | 98.6 | 310 |
| Fever threshold | 38 | 100.4 | 311 |
| Heatwave | 40 | 104 | 313 |
| Water boils | 100 | 212 | 373.15 |
Oven temperature chart
Recipes often give an oven setting in the other scale, or as a UK gas mark. These are the conventional rounded equivalents cooks use. If you have a fan or convection oven, set it about 20°C (roughly 25 to 30°F) lower than the figure shown.
| Oven setting | °C | °F | Gas mark |
|---|---|---|---|
| Cool | 140 | 275 | 1 |
| Warm | 150 | 300 | 2 |
| Moderate | 180 | 350 | 4 |
| Moderately hot | 190 | 375 | 5 |
| Hot | 200 | 400 | 6 |
| Very hot | 220 | 425 | 7 |
| Hottest | 240 | 475 | 9 |
For a one page version to keep by the oven, open the printable oven temperature chart.
Where temperature conversion comes up
Temperature is one of the few measurements where two everyday scales are still in active use, so conversions appear constantly. Knowing which scale you are starting from, and which one you need, is half the job.
Weather and travel. A forecast in Fahrenheit means little if you think in Celsius, and the other way around. The everyday table above turns a number into a feel: 30°C is a warm day, 40°C is a heatwave.
Cooking and baking. Recipes cross borders freely. A cake at 180°C is the same as 350°F or gas mark 4, but a fan oven needs a lower setting. Getting this right matters more for baking than for roasting.
Science and study. Lab and physics work uses Kelvin because it has no negative values and starts at absolute zero, which keeps the maths clean. A degree change is identical in Celsius and Kelvin, so only the starting point shifts.
Workshop and 3D printing. Filament data sheets, hotend targets and bed temperatures are usually in Celsius, but tools and guides written for a US audience often quote Fahrenheit. A quick conversion avoids a failed first layer.
Health. Normal body temperature is about 37°C or 98.6°F, and a fever starts near 38°C or 100.4°F. Converting a reading helps you understand a thermometer that uses the other scale, though medical decisions should always involve a professional.
Frequently Asked Questions
Which temperature converter should I use?
For weather, cooking and body temperature, use Celsius to Fahrenheit or Fahrenheit to Celsius. For school, lab or physics work that needs absolute temperature, use Celsius to Kelvin or Kelvin to Celsius. If you only know the value you have and the value you want, pick the converter named in that direction and the result is instant.
What is the quickest way to estimate Celsius to Fahrenheit in my head?
Double the Celsius number and add 30. So 20°C is roughly 70°F and 25°C is roughly 80°F. The exact values are 68°F and 77°F, so the estimate runs a few degrees high, but it is close enough to judge whether you need a jacket. For anything precise, use the exact formula °F = (°C × 9/5) + 32.
Why does science use Kelvin instead of Celsius?
Kelvin starts at absolute zero, the point where molecular motion stops, so it never has negative numbers. That keeps equations in physics and chemistry clean, especially the gas laws where temperature appears as a direct multiplier. A change of one kelvin is exactly the same size as a change of one degree Celsius, so converting is just adding or subtracting 273.15.
At what temperature do Celsius and Fahrenheit read the same?
They meet at exactly −40°. That is the single point where −40°C and −40°F describe the same temperature. Above it, the Fahrenheit number is larger; below it, the Fahrenheit number is smaller than the Celsius number.
How do I convert a fan or convection oven temperature?
Convert the temperature normally first, then lower the result by about 20°C (roughly 25 to 30°F) for a fan oven, because moving air heats food faster. A recipe calling for 180°C in a conventional oven becomes about 160°C in a fan oven. Many newer ovens show both settings or adjust automatically.
Is a degree Celsius the same size as a degree Kelvin or Fahrenheit?
A Celsius degree and a kelvin are exactly the same size; only the zero point differs by 273.15. A Fahrenheit degree is smaller: one degree Celsius equals 1.8 degrees Fahrenheit. That is why the Celsius to Fahrenheit formula multiplies by 9/5 before adding the 32 degree offset.