Temperature Unit Converter
Convert between Celsius, Fahrenheit, Kelvin and Rankine with the exact affine formulas — not a rough approximation.
How it works
°F = °C × 9/5 + 32 · K = °C + 273.15 · °R = (°C + 273.15) × 9/5 · °C = (°F − 32) × 5/9
Temperature scales are affine, not simply proportional, so you cannot convert by a single multiply — each scale has both a different degree size and a different zero point. Celsius and Kelvin share the same degree size but Kelvin starts at absolute zero (−273.15 °C). Fahrenheit and Rankine share the smaller Fahrenheit degree, with Rankine measured from absolute zero. This tool converts everything through Celsius so all four scales stay exact.
Worked example
Convert 100 °C to Fahrenheit: 100 × 9/5 + 32 = 180 + 32 = 212 °F, the boiling point of water. In Kelvin that same temperature is 100 + 273.15 = 373.15 K.
Sources: Temperature conversion — Wikipedia
Frequently asked questions
What is the formula from Celsius to Fahrenheit?
Multiply the Celsius value by 9/5 (i.e. 1.8) and add 32. So 20 °C = 20 × 1.8 + 32 = 68 °F. To go the other way, subtract 32 first, then multiply by 5/9.
What is Rankine and who uses it?
Rankine is an absolute temperature scale that uses Fahrenheit-sized degrees, so 0 °R is absolute zero and water freezes at 491.67 °R. It appears in some US engineering and thermodynamics work where absolute temperature is needed but Fahrenheit degrees are the convention.
At what temperature do Celsius and Fahrenheit read the same?
At −40°, where −40 °C equals −40 °F exactly. It is the single point where the two scales cross.
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This calculator is for educational purposes. Double-check important results before acting on them.