Convert temperature between Celsius, Fahrenheit and Kelvin with exact formulas — °F = °C × 9/5 + 32, K = °C + 273.15. Free, in your browser.
How temperature conversion works
Temperature is the one everyday conversion you can't do with a single multiplication, because the scales don't share a zero point: 0 °C is the freezing point of water, 0 °F is a brine freezing point, and 0 K is absolute zero. Each conversion is affine — a scale factor plus an offset. The converter goes through Celsius: Fahrenheit is °C × 9/5 + 32, and Kelvin is °C + 273.15 with no scale change, since a kelvin is the same size as a Celsius degree. The scales cross at exactly −40, where −40 °C = −40 °F.
°F = °C × 9/5 + 32 · K = °C + 273.15 · −40 °C = −40 °FFrequently asked questions
Is anything I enter uploaded anywhere?
No. The formulas run locally in your browser — nothing you type is sent to a server, logged or stored. Only the value and selected scales appear in the URL so you can share a preconfigured conversion.
Why can't temperature be converted with a simple factor?
Because the scales start from different zero points. Converting metres to feet only needs a ratio, but 0 °C and 0 °F are different temperatures, so the conversion needs an offset too: °F = °C × 9/5 + 32. That offset is why doubling a Celsius value does not double the Fahrenheit one.
What is Kelvin used for?
Kelvin is the SI unit of thermodynamic temperature, used in science because it starts at absolute zero (−273.15 °C), the point where no more heat can be removed. A kelvin step equals a Celsius step, so converting is just adding 273.15 — and Kelvin values are never negative.
Last updated: 8 July 2026
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