Convert Celsius, Fahrenheit and Kelvin with the exact formula shown for every conversion.
Temperature is the one everyday conversion that cannot be done with a single multiplier. Length, weight and volume are proportional — double the metres and you double the feet — but the temperature scales do not share a zero, so each conversion has to scale the value and then shift it. That is why °F = °C × 9/5 + 32 and K = °C + 273.15, and why this tool prints the exact formula it applied next to every answer instead of just handing you a number.
The three scales are three different historical answers to the same question. Daniel Fahrenheit set his 1724 scale with 0 at the temperature of a brine of ice, water and salt and roughly 96 for human body temperature, which is how water ended up freezing at the awkward 32 and boiling at 212. Anders Celsius proposed his hundred-degree scale in 1742 with the numbers the other way round — 0 for boiling, 100 for freezing — and it was inverted to today's form shortly after his death. William Thomson, Lord Kelvin, proposed an absolute scale in 1848 that starts where thermal motion stops; since 2019 the kelvin has been defined from the Boltzmann constant rather than from water, which is why it carries no degree sign: it measures an absolute quantity, not a position between two arbitrary marks. One consequence of the arithmetic is a curiosity the reference table shows: at −40 the Celsius and Fahrenheit scales cross and read exactly the same.
In practice, the conversions people actually look up are few. A fever of 38 °C is 100.4 °F, an oven at 180 °C is 356 °F, a comfortable room at 21 °C is about 70 °F, and body temperature at 37 °C is 98.6 °F. Kelvin shows up in physics, astronomy and photography, where the colour temperature of a light source is quoted in K. The converter also warns you when a value falls below absolute zero — −273.15 °C, or 0 K — because no temperature can be colder than that. Everything runs in your browser: nothing you type is transmitted or stored.
°F = °C × 9/5 + 32 · °C = (°F − 32) × 5/9 · K = °C + 273.15 · °C = K − 273.15. The scales are affine, not proportional: every conversion both scales the value and shifts its zero.
Double the Celsius value and add 30 for a rough figure — 20 °C becomes about 70 °F, close to the exact 68 °F. The precise formula is °C × 9/5 + 32.
At −40. Minus forty degrees Celsius is exactly minus forty degrees Fahrenheit, the single point where the two scales cross.
Because it is an absolute scale, not a position between two chosen reference points. It is written 298.15 K, never 298.15 °K, and its zero is the coldest temperature that can exist: −273.15 °C.
38 °C, the usual clinical threshold, is 100.4 °F. Normal body temperature of 36.5 °C to 37 °C corresponds to 97.7 °F to 98.6 °F.
Yes. Use a minus sign, and either a comma or a dot for decimals — "−12,5" and "-12.5" are both read as the same value.
No. The conversion is pure JavaScript running on your device, with no network request of any kind.
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