Temperature Converter

Most unit conversions, like length or weight, use a single multiplying factor because both scales share the same zero point. Temperature scales don't: Celsius, Fahrenheit, and Kelvin each start counting from a different point. That mismatch means you need to both scale the number and shift it by an offset, which is why the formulas include addition or subtraction alongside multiplication.

A Kelvin and a Celsius degree represent the same size of temperature change, so a 1-degree rise in one equals a 1-degree rise in the other. The only difference is where zero sits: Celsius zero is water's freezing point, while Kelvin zero is absolute zero, the lowest temperature theoretically possible. To convert, simply add 273.15 to a Celsius value.

Rankine is an absolute scale, like Kelvin, but it uses Fahrenheit-sized degrees instead of Celsius-sized ones. It shows up occasionally in some engineering and thermodynamics contexts in the United States, particularly in older reference tables, but it is far less common today than Celsius, Fahrenheit, or Kelvin in everyday and scientific use.

Réaumur is an older temperature scale that sets water's freezing point at 0 degrees and its boiling point at 80 degrees, compared with 100 degrees on the Celsius scale. It was once widely used in parts of Europe but has largely been replaced by Celsius. You can still convert to and from it here if you encounter it in historical records or instruments.

This converter is built for absolute temperature readings, like the current air temperature or an oven setting, and applies the full offset formulas accordingly. If you're converting how much a temperature changed rather than a specific point, the offsets cancel out and only the scaling factor applies, which is a different calculation from the one used here.