Temperature Converter

Convert temperatures between Celsius, Fahrenheit, Kelvin and Rankine, with the formula and reference points for freezing, body temperature and boiling.

How to use the temperature Converter

  1. Enter the value.
  2. Choose the from from the list.
  3. Choose the to from the list.
  4. The result updates instantly as you type. There is no button to press.
  5. Use Copy result to copy the figures, or Copy link to share a link that reopens the temperature Converter with the same inputs.

How it works

Temperature conversions are trickier than most unit changes because the scales don't share a zero point, so you can't just multiply. Celsius sets 0° at the freezing point of water and 100° at its boiling point at sea level. Fahrenheit, still used for weather and cooking in the United States, puts those same points at 32° and 212°, so each Fahrenheit degree is 5/9 the size of a Celsius degree, and the scales are offset by 32.

Kelvin is the scientific scale. It uses Celsius-sized degrees but starts at absolute zero, the lowest possible temperature, where particles have the minimum possible energy. 0 K is −273.15 °C, and kelvins are written without a degree sign. Rankine is the Fahrenheit equivalent of kelvin, starting at absolute zero with Fahrenheit-sized degrees, and is still used in some US engineering.

This converter changes your value to kelvin first, then to the target scale, so every pair of scales is handled with the same exact formulas. It also refuses values below absolute zero, which can't physically exist. One handy fact: −40 is the same in Celsius and Fahrenheit.

Formula

°F = °C × 9/5 + 32 °C = (°F − 32) × 5/9 K = °C + 273.15 °R = °F + 459.67 = K × 9/5

Example

25 °C × 9/5 = 45, plus 32 = 77 °F, a warm day. A fever of 101 °F is (101 − 32) × 5/9 = 38.3 °C. An oven at 180 °C is 356 °F, usually rounded to 350 °F in recipes. Room temperature of 20 °C is 293.15 K.

Frequently asked questions

What is a quick way to convert Celsius to Fahrenheit?

Double the Celsius figure and add 30. It gives 80 °F for 25 °C, close to the true 77 °F, and works best for everyday weather temperatures.

At what temperature are Celsius and Fahrenheit equal?

At −40. −40 °C is exactly −40 °F.

Why doesn't kelvin use a degree symbol?

Kelvin is an absolute scale and an SI base unit, so temperatures are written as 300 K, not 300 °K. The degree sign was officially dropped in 1967.