Temperature Converter
Convert between Celsius, Fahrenheit, Kelvin, and Rankine.
- celsius
- fahrenheit
- kelvin
- temperature
- c
- f
- k
About Temperature Converter
Temperature is unusual among unit conversions because the scales don't share a zero point. Doubling a length in metres really does double the distance — but doubling 10 °C doesn't double the heat content, because Celsius zero is arbitrary (it's the freezing point of water, not absolute zero). That's why each Celsius-to-Fahrenheit or Celsius-to-Kelvin conversion involves both a multiplication and an offset.
This converter handles Celsius, Fahrenheit, Kelvin, and Rankine — the four temperature scales you'll encounter in everyday life, science, engineering, and old American technical references. Each conversion uses the standard formula, so the values match what you'll find in a physics textbook or an oven manual.
How to use
Type a temperature into the input and pick the scale from the dropdown beside it. The conversions panel below shows the same temperature in every other scale — useful for recipes that switch between Fahrenheit and Celsius, weather forecasts in unfamiliar units, or scientific work that needs Kelvin.
Tap any row in the conversions list to switch the input to that scale. The default value (20 °C) is a comfortable room temperature, which makes a good sanity check: it should come out as 68 °F, 293.15 K, and 527.67 °R.
Frequently asked questions
How do I convert Celsius to Fahrenheit in my head?
Multiply by 1.8 (or 9/5) and add 32. For quick mental work, double the Celsius value and add 30 — close enough for everyday weather (20 °C ≈ 70 °F, 30 °C ≈ 90 °F). The 32 °F freezing point and 100 °C / 212 °F boiling point are the two anchors worth memorising.
What is absolute zero?
Absolute zero is 0 K, equivalent to −273.15 °C or −459.67 °F. It's the theoretical point at which all molecular motion stops; nothing in the universe is colder. The Kelvin scale uses absolute zero as its zero point, which is why Kelvin temperatures are always positive.
When would I use Kelvin?
In any physics or chemistry calculation involving thermodynamics — ideal gas laws, blackbody radiation, reaction rates — because doubling the Kelvin temperature really does double the absolute thermal energy, whereas Celsius and Fahrenheit have arbitrary zero points. Kelvin is also used to describe the colour temperature of light sources (e.g. 6500 K daylight, 2700 K incandescent).
What is the Rankine scale?
Rankine is to Fahrenheit what Kelvin is to Celsius: it shares Fahrenheit's degree size but starts at absolute zero. So 0 °R is absolute zero and 491.67 °R is the freezing point of water. It's still used in some US thermodynamic and aerospace engineering contexts; everyone else uses Kelvin.