Temperature Interval Converter

Absolute temperature scales like Celsius and Fahrenheit each have their own zero point, set at different physical conditions, so converting an actual temperature reading requires shifting by an offset as well as scaling. An interval is different: it only describes the size of a change, so the offset cancels out entirely and only the scale factor between degree sizes matters. A rise of 10 °C is the same physical change as a rise of 10 K, because the Celsius and kelvin scales use identically sized degrees, just with different starting points.

Because Fahrenheit and Rankine degrees are smaller than Celsius and kelvin degrees, the same physical change corresponds to a larger number of Fahrenheit or Rankine degrees. Specifically, one Fahrenheit degree of change equals five ninths of a kelvin, so converting a Celsius or kelvin interval into Fahrenheit or Rankine multiplies by 1.8, and converting the other way divides by 1.8. Réaumur degrees follow their own historical scale, where one Réaumur degree equals 1.25 kelvin.

Choose the interval's starting unit and target unit in the from and to menus, enter the size of the change, and the result appears immediately. A table shows the same interval expressed in every supported unit at once, a precision control adjusts how many decimal places are shown, and a swap button reverses the two selected units in one click.

Suppose a furnace's temperature rises by 45 °C during a cycle and you want that change expressed in Fahrenheit degrees. Since this is an interval, there's no offset to worry about: multiply the Celsius change by 1.8, because each Fahrenheit degree is smaller than a Celsius degree. That gives 45 × 1.8 = 81 °F of change.

Typing 45 into the °C field with °F selected as the target returns 81 °F immediately, confirming the calculation. The full unit table also shows that same 45 °C rise equals 45 K and 36 °Ré, all derived from one entered value without ever touching an absolute temperature scale or its zero point.