How the Temperature Converter works
Celsius and Kelvin use degrees of the same size, as do Fahrenheit and Rankine. A Celsius degree is 9/5 (1.8) times the size of a Fahrenheit degree. The scales differ only in where zero is: Kelvin and Rankine start at absolute zero, Celsius starts at the freezing point of water (273.15 K) and Fahrenheit's zero is 459.67 °R.
The converter uses a direct formula for each pair of scales, for example °F = °C × 9/5 + 32 and K = (°F + 459.67) × 5/9, and shows the formula and the calculation with your number. Results are rounded in decimal to the number of decimal places you choose. If the value is colder than absolute zero (−273.15 °C, −459.67 °F, 0 K or 0 °R) you get a warning, because no real temperature can be that low.
How to use the Temperature Converter
- Type a temperature in the Temperature box. Negative values and decimals are allowed.
- Choose its scale: Celsius, Fahrenheit, Kelvin or Rankine.
- Choose how many decimal places to show.
- Read the result in the other three scales. The Formulas used table shows each formula and the calculation with your number.
- Select Copy under a result to copy the number.
Example
Entering 100 with Celsius (°C) selected gives:
°C → °F °F = °C × 9/5 + 32 100 × 9/5 + 32 = 212
°C → K K = °C + 273.15 100 + 273.15 = 373.15
°C → °R °R = (°C + 273.15) × 9/5 (100 + 273.15) × 9/5 = 671.67Entering 98.6 °F gives 37 °C, 310.15 K and 558.27 °R.
Common use cases
- Following a recipe or oven setting written in a different scale.
- Reading weather forecasts, thermostat settings or body temperatures from another country.
- Converting between Celsius and Kelvin for physics, chemistry or sensor data.
- Working with Rankine values in US engineering thermodynamics tables.
Frequently asked questions
How do I convert Celsius to Fahrenheit?
Multiply by 9/5 (1.8) and add 32. For example, 25 °C × 9/5 + 32 = 77 °F. To go back, subtract 32 and multiply by 5/9.
What is the Rankine scale?
Rankine is an absolute scale with Fahrenheit-sized degrees: 0 °R is absolute zero and water freezes at 491.67 °R. It is used mainly in some US engineering fields. To convert, add 459.67 to a Fahrenheit value.
Why do I get a warning for some values?
Nothing can be colder than absolute zero: 0 K, −273.15 °C, −459.67 °F or 0 °R. If you enter a lower value, the converter still shows the arithmetic but warns that the temperature is not physically possible.
At what temperature are Celsius and Fahrenheit equal?
At −40. −40 °C is exactly −40 °F.
Should Kelvin be written with a degree sign?
No. Since 1968 the unit is simply kelvin, written K without a degree sign, for example 300 K.