Temperature Converter
Convert temperature between Celsius, Fahrenheit, Kelvin, and Rankine instantly.
How to use this tool
- Enter temperature and from unit in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your fahrenheit and the full breakdown beneath it.
Formula
All conversions pass through Celsius as the intermediate unit.
To Celsius: °F → °C: (°F − 32) × 5/9 | K → °C: K − 273.15 | °R → °C: (°R − 491.67) × 5/9
From Celsius: °C → °F: °C × 9/5 + 32 | °C → K: °C + 273.15 | °C → °R: °F + 459.67
How it works
The calculator first converts the input to Celsius using the appropriate offset-and-scale formula, then derives Fahrenheit, Kelvin, and Rankine from that Celsius value in a single pass. Kelvin and Rankine are absolute scales (zero = absolute zero), while Celsius and Fahrenheit are offset scales anchored to water's freezing and boiling points.
A very common mistake is applying only the scale factor without the offset: multiplying 100 °C by 9/5 gives 180, but the correct Fahrenheit value is 180 + 32 = 212 °F. Forgetting the additive offset is the most frequent source of temperature conversion errors.
Worked example
Convert 100 °C to all temperature units
- Input: 100 °C (from_unit = celsius), so Celsius = 100.
- Fahrenheit: 100 × 9/5 + 32 = 180 + 32 = 212 °F.
- Kelvin: 100 + 273.15 = 373.15 K.
- Rankine: 212 + 459.67 = 671.67 °R.
212 °F | 373.15 K | 671.67 °R
Common mistakes to avoid
- Forgetting to subtract 32 before multiplying when converting Fahrenheit to Celsius — a common shortcut error yields answers off by ~17 degrees.
- Treating Kelvin as if it can go negative; Kelvin starts at 0 (absolute zero) and negative Kelvin values are physically meaningless.
- Confusing Rankine with Kelvin — both are absolute scales but Rankine uses Fahrenheit-sized degrees, so the numeric values differ by a factor of 9/5.
Key terms
- Celsius (°C)
- A temperature scale where 0 is the freezing point of water and 100 is its boiling point at standard atmospheric pressure.
- Fahrenheit (°F)
- The temperature scale used in the United States, where water freezes at 32 °F and boils at 212 °F.
- Kelvin (K)
- The SI absolute temperature scale. 0 K is absolute zero (−273.15 °C); it uses the same degree size as Celsius.
- Rankine (°R)
- An absolute temperature scale used in some US engineering contexts, with degree intervals equal to Fahrenheit. 0 °R = absolute zero = −459.67 °F.
Frequently asked questions
- What is absolute zero in Celsius and Fahrenheit?
- Absolute zero is 0 K, which equals -273.15 degrees C and -459.67 degrees F. It is the theoretical temperature at which all molecular motion stops.
- Why does the formula subtract 32 when converting Fahrenheit to Celsius?
- The Fahrenheit and Celsius scales have different zero points. Water freezes at 32 degrees F but 0 degrees C, so you subtract 32 to align the baselines before applying the 5/9 ratio.
- When would I use Rankine instead of Kelvin?
- Rankine is used in some engineering fields in the United States that use imperial units throughout. It keeps the absolute-zero baseline while using Fahrenheit-sized degree steps.