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Temperature Converter
Convert Celsius, Fahrenheit and Kelvin, including oven and weather figures.
A recipe from a US food blog says to bake at 350°F. Your oven dial only shows Celsius and gas marks. Get the conversion wrong by even one digit and a cake that needed 175°C either burns or comes out raw in the middle.
The oven problem, solved properly
Fahrenheit to Celsius is: subtract 32, then multiply by 5/9. So 350°F minus 32 is 318, times 5/9 is 176.7°C, which any home baker rounds to 175°C. Going the other way, multiply Celsius by 9/5 and add 32.
UK recipes complicate things further with gas marks, a scale that only exists on British and Irish cookers. Gas mark 4 is 180°C (350°F), gas mark 6 is 200°C (400°F), and each mark up or down is roughly a 14°C step — not a formula so much as a lookup table cooks memorise.
Reference points worth knowing
| Celsius | Fahrenheit | Kelvin | What it is |
|---|---|---|---|
| −273.15° | −459.67° | 0 | Absolute zero |
| −40° | −40° | 233.15 | The only point the two scales agree |
| 0° | 32° | 273.15 | Water freezes |
| 37° | 98.6° | 310.15 | Human body temperature |
| 100° | 212° | 373.15 | Water boils at sea level |
Why Kelvin has no negative numbers
Kelvin does not measure temperature relative to freezing water like Celsius does. It measures it relative to absolute zero, the coldest anything can theoretically get, where atomic motion stops almost entirely. That makes 0 K the floor of the scale — there is no such thing as a negative Kelvin temperature in classical physics, which is why scientific instruments and equations default to it instead of Celsius.
A Kelvin degree and a Celsius degree are the same size, so converting between them is just addition: add 273.15 to a Celsius figure to get Kelvin. Converting to or from Fahrenheit is the only case that needs the 5/9 or 9/5 multiplier, because Fahrenheit degrees are a different size — 180 of them span the same range as 100 Celsius degrees.
Temperature conversion questions
What temperature is the same in Celsius and Fahrenheit?
−40°. Both scales cross at exactly that point, which makes it a handy check — if a conversion calculation gives a different answer at −40 on both sides, something in the formula is wrong.
How do I convert Celsius to Fahrenheit in my head?
A rough shortcut is to double the Celsius figure and add 30; it is not exact but gets you within a few degrees, which is close enough for deciding what to wear. For an exact figure, multiply by 9/5 and add 32.
Why does the US still use Fahrenheit?
Mostly historical inertia. The US began adopting Fahrenheit widely in the 18th century and never made the switch to Celsius that almost every other country made during metrication in the mid-20th century, so it persists in weather, cooking and everyday conversation.
What is gas mark 4 in Celsius and Fahrenheit?
Gas mark 4 is 180°C, or 350°F, one of the most common baking temperatures on British recipes. Each gas mark step up or down corresponds to roughly a 14°C change in oven temperature.
Why is Kelvin used in science instead of Celsius?
Because many physical laws, particularly in thermodynamics and gas behaviour, are much simpler to express relative to absolute zero rather than to the freezing point of water. Kelvin also avoids negative numbers in most practical scientific ranges, which simplifies calculations.
