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Temperature converter

Celsius, Fahrenheit, Kelvin and Rankine, converted with the exact offset formulas and a common-values table.

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Temperature scales differ in both the size of a degree and where zero sits, so converting needs an offset as well as a factor. The exact relations are °F = °C × 9/5 + 32, K = °C + 273.15 and °R = °F + 459.67, where the Rankine scale is the absolute scale with Fahrenheit-sized degrees still found in some US engineering tables. This converter uses kelvin internally and shows the textbook formula for the pair you pick.

Common reference points: water freezes at 0 °C (32 °F) and boils at 100 °C (212 °F) at sea level; normal body temperature is usually quoted as 37 °C (98.6 °F); −40 is the same in both scales; absolute zero is 0 K, −273.15 °C or −459.67 °F. The converter warns you if a value falls below absolute zero, which is physically impossible.

Because of the offset, temperature differences convert differently from temperatures: a rise of 10 °C is a rise of 18 °F, not 50 °F.

How to use it

  1. Choose the scale you have and the scale you want.
  2. Type the temperature in either box (negative values are fine).
  3. Check the formula line and the table of common temperatures below.

Frequently asked questions

What is the formula to convert Celsius to Fahrenheit?

Multiply by 9/5 (1.8) and add 32: 25 °C × 1.8 + 32 = 77 °F. The reverse is °C = (°F − 32) × 5/9.

Why is there no degree sign on kelvin?

The kelvin is an SI base unit defined on an absolute scale, so it is written "K" without "degree" (since 1967). 0 K is absolute zero and a change of 1 K equals a change of 1 °C.

How do I convert a temperature difference?

Multiply only, without the offset: a difference of 5 °C equals 9 °F (5 × 9/5) and 5 K. Use this for things like "the room warmed by 3 °C".

At what temperature are Celsius and Fahrenheit equal?

At −40: −40 °C = −40 °F. Solve x = x × 9/5 + 32 and you get x = −40.

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