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Temperature Converter

Convert temperatures between Celsius, Fahrenheit, Kelvin and Rankine.

Enter a temperature in any scale and see its equivalent in the others, with the conversion formula displayed so you can verify it by hand. Handles negative values and very large/small inputs without rounding artefacts.

Common use cases: cooking and baking when a recipe uses the other scale, weather forecasts on travel, scientific calculations that demand Kelvin, and double-checking the result of a quick mental conversion.

Frequently asked questions

What's the formula behind C ↔ F?
F = C × 9/5 + 32 and C = (F − 32) × 5/9. The two scales coincide at -40 (same number on both). 0°C is the freezing point of water at sea level; 100°C is its boiling point. 32°F and 212°F are the same two reference points.
Why are there three scales at all?
Historical accident. Fahrenheit was first (1724), based on a brine mixture and human body temperature. Celsius (1742) anchored on water's phase changes. Kelvin (1848) anchored on absolute zero — the temperature at which molecular motion stops — making it the only scale where temperature ratios are physically meaningful.
When should I use Kelvin?
For any physical or chemical calculation involving the gas laws, blackbody radiation, or thermodynamics — anywhere a temperature ratio matters. 2 × 273 K = 546 K is meaningful (twice as hot in an absolute sense); 2 × 0°C = 0°C is meaningless.
What about Rankine?
Rankine is to Fahrenheit what Kelvin is to Celsius — anchored at absolute zero, same step size as Fahrenheit. Used in some US engineering disciplines (jet engines, HVAC). Rarely seen outside those domains.

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