Temperature Converter
Convert Celsius to Fahrenheit, Fahrenheit to Celsius and either to Kelvin — with a plain-English note on what the temperature actually means.
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Weather, body and oven reference
The temperatures that come up most — freezing, room temperature, body heat, boiling and oven settings — in the two scales you've selected.
The formulas
Temperature is the one conversion on this site that isn't a simple multiplication, because the scales don't share a zero. Celsius puts zero at the freezing point of water; Fahrenheit puts it 32 degrees lower; Kelvin puts it at absolute zero. So every conversion needs both a stretch and a shift:
| Conversion | Formula |
|---|---|
| Celsius → Fahrenheit | °F = (°C × 9/5) + 32 |
| Fahrenheit → Celsius | °C = (°F − 32) × 5/9 |
| Celsius → Kelvin | K = °C + 273.15 |
| Kelvin → Celsius | °C = K − 273.15 |
| Fahrenheit → Kelvin | K = (°F − 32) × 5/9 + 273.15 |
The 9/5 is the stretch: a Fahrenheit degree is smaller than a Celsius degree, so it takes 1.8 of them to cover the same amount of warming. The 32 is the shift. Getting the order wrong — adding 32 before multiplying instead of after — is the classic mistake, and it's why so many people mis-convert oven temperatures.
The one place the scales agree
−40 °C and −40 °F are the same temperature. It's the single point where the two lines cross, and it's genuinely useful to know: if you ever see a temperature quoted as −40 and no unit given, it doesn't matter.
Doing it in your head
The exact formula is awkward to do while someone is talking to you. Two shortcuts:
- Celsius to Fahrenheit: double it and add 30. 20 °C → 70 °F (true: 68). 25 °C → 80 °F (true: 77). It drifts high as temperatures rise, but for weather it's fine.
- Fahrenheit to Celsius: subtract 30 and halve. 70 °F → 20 °C (true: 21). 90 °F → 30 °C (true: 32).
For anything that matters — an oven, a fever, a lab — use the real formula or the converter above. The shortcut is for deciding what to wear.
Oven temperatures and gas marks
Recipe conversion is where this page earns its keep. British recipes often give gas marks, American ones give Fahrenheit, and most modern ovens want Celsius — and fan ovens want something different again:
| Description | °C (conventional) | °C (fan) | °F | Gas mark |
|---|---|---|---|---|
| Very cool | 140 | 120 | 275 | 1 |
| Cool | 150 | 130 | 300 | 2 |
| Warm | 160 | 140 | 325 | 3 |
| Moderate | 180 | 160 | 350 | 4 |
| Fairly hot | 190 | 170 | 375 | 5 |
| Hot | 200 | 180 | 400 | 6 |
| Very hot | 220 | 200 | 425 | 7 |
| Hottest | 240 | 220 | 475 | 9 |
The fan column matters more than people realise. A fan oven circulates hot air, so it cooks faster at the same dial setting — the usual rule is to drop the temperature by about 20 °C from what a conventional recipe asks for. Ignore that and things brown on the outside before they're cooked through.
Kelvin, and why there are no degrees
Kelvin starts at absolute zero, the point where there is no thermal energy left to remove. Nothing can be colder, which is why this page refuses temperatures below −273.15 °C. Because the scale has a true zero rather than an arbitrary one, kelvin is written without the degree symbol — 300 K, not 300 °K. A change of one kelvin is exactly the same size as a change of one degree Celsius, which is why converting between them is just addition.
Frequently asked questions
What is the formula for Celsius to Fahrenheit?
°F = (°C × 9/5) + 32. Multiply first, then add — doing it the other way round is the most common mistake and it'll put your oven roughly 30 degrees out. For a rough answer in your head, double the Celsius and add 30.
At what temperature are Celsius and Fahrenheit the same?
Minus 40. −40 °C and −40 °F are the same temperature, and it's the only point where the two scales meet. Above it Fahrenheit is the larger number; below it, Celsius is.
What is 180 °C in Fahrenheit for baking?
356 °F, which almost every recipe rounds to 350 °F — that's the standard moderate oven. If you have a fan oven, drop it to about 160 °C, because circulating air cooks faster at the same dial setting. There's a full oven table above including gas marks.
Why is Kelvin written without a degree symbol?
Because it's an absolute scale with a true zero, rather than one defined against arbitrary reference points. The convention is 300 K, not 300 °K. One kelvin and one degree Celsius are the same size, so converting between them is simply adding or subtracting 273.15.
Can a temperature be below absolute zero?
No. Absolute zero (0 K, −273.15 °C, −459.67 °F) is the point where a substance has no thermal energy left to give up. This converter will tell you if you enter something colder, because the number would be physically meaningless.
Are my numbers sent anywhere?
No. Everything is worked out inside your own browser. Nothing you type is uploaded, stored or shared, and there's no sign-up.
Related calculators
Please note: CalcuLane uses the internationally agreed definitions, which are exact for length, weight, temperature, volume, speed and data. Shoe sizing is a convention rather than a measurement and varies between brands, so treat those results as a starting point. Where precision genuinely matters, confirm against an authoritative source.