Temperature Converter (°C, °F, K, °R)
Convert temperature between Celsius, Fahrenheit, Kelvin, and Rankine — enter one value and see it in every scale, with a table of notable temperatures.
Notable temperatures
| Reference point | °C | °F | K | °R |
|---|---|---|---|---|
| Absolute zero | -273.15 | -459.67 | 0 | 0 |
| Water freezes | 0 | 32 | 273.15 | 491.67 |
| Room temperature | 20 | 68 | 293.15 | 527.67 |
| Body temperature | 37 | 98.6 | 310.15 | 558.27 |
| Water boils (sea level) | 100 | 212 | 373.15 | 671.67 |
Converting temperature scales
Temperature is unusual among unit conversions because the scales don't just differ in size — they start counting from different places. Celsius and Kelvin share the same step size but Kelvin's zero is absolute zero, the coldest possible temperature, 273.15 degrees below the freezing point of water. Fahrenheit uses both a different zero and a smaller degree. So a conversion isn't a single multiplication; it needs an offset too.
°F = °C × 9/5 + 32 · K = °C + 273.15
°C = (°F − 32) × 5/9 · °R = K × 9/5
Kelvin is the SI unit, used in science and for anything involving absolute temperature; it has no degree symbol. Rankineis its Fahrenheit-sized cousin — absolute zero counted in Fahrenheit-sized degrees — and still turns up in some US engineering.
Worked example and the −40 trick
Body temperature is 37 °C: 37 × 9/5 + 32 = 98.6 °F, or 37 + 273.15 = 310.15 K. A useful landmark is that the Celsius and Fahrenheit scales cross at exactly −40° — −40 °C and −40 °F are the same temperature — which is a quick way to sanity-check any conversion.
Absolute zero and negative Kelvin
Because Kelvin and Rankine start at absolute zero, they can never be negative. If a conversion gives you a negative Kelvin value, the input was below absolute zero and isn't physically possible — a handy check when you're working from a measured figure.
A temperature difference converts differently
These conversions are for absolute temperatures, which carry an offset: °C = (°F − 32) × 5/9. A temperature differencedoes not carry that offset — a rise of 180 °F is a rise of 100 °C, not 82.2 °C. Anywhere a calculation takes a ΔT, such as heating or thermal expansion, multiply by 5/9 and leave the 32 alone. Using the absolute formula on a difference is a silent error of about 18 degrees.