Temperature Converter
Temperature scales have different zero points, so they need offsets rather than simple factors. The formula used is shown with every conversion.
All scales
Reference points
How to use the Temperature Converter
- Enter a temperature and choose the scale it is in.
- Pick the scale you want it converted to.
- The formula used appears underneath, along with every other scale and a set of reference points.
The formulas
| Conversion | Formula |
|---|---|
| Celsius → Fahrenheit | (°C × 9/5) + 32 |
| Fahrenheit → Celsius | (°F − 32) × 5/9 |
| Celsius → Kelvin | °C + 273.15 |
| Fahrenheit → Rankine | °F + 459.67 |
Temperature is the one common conversion that needs an offset, not just a factor. That is because Celsius and Fahrenheit put their zero points in different places — which is also why you cannot convert a temperature difference the same way. A rise of 10 °C is a rise of 18 °F, not 50 °F.
Why −40 is the same in both
Setting the two scales equal and solving gives exactly one crossing point: −40 °C = −40 °F. It is a genuinely useful fact in cold climates, where an unlabelled −40 needs no conversion.
A quick mental approximation for everyday temperatures: double the Celsius figure and add 30. For 20 °C that gives 70 °F against a true 68 — close enough for deciding on a jacket. The error grows at the extremes, so use the exact formula for cooking or anything technical.
Kelvin and absolute zero
Kelvin starts at absolute zero, the point where thermal motion is minimal, and uses the same degree size as Celsius. It takes no degree symbol — 300 K, not 300 °K — and it is the SI base unit for temperature.
Rankine does the same thing with Fahrenheit-sized degrees, starting at −459.67 °F. It survives mainly in US engineering thermodynamics. Because both scales are absolute, a negative value in either is physically impossible, which is why this tool rejects it.
Frequently asked questions
What is 98.6 °F in Celsius?
Exactly 37 °C. The famous 98.6 is a conversion artefact — the original 19th-century measurement was 37 °C, and converting it produced a figure that looks more precise than the underlying data was.
Why does Kelvin have no degree symbol?
Because it is an absolute scale rather than a relative one. The SI convention is 300 K, written and spoken as "300 kelvin".
Can I convert a temperature difference?
Not with these formulas. For a difference, use the ratio alone: 1 °C of change equals 1.8 °F of change and exactly 1 K of change.
Which countries use Fahrenheit?
The United States and a handful of territories. Almost everywhere else uses Celsius for weather and cooking, with Kelvin reserved for scientific work.
Related tools
Convert between metric and imperial length units.
Convert between kilograms, pounds, ounces, stone and tonnes.
Convert km/h, mph, m/s, knots and Mach.
Convert between binary, octal, decimal, hex and any base 2–36.
Five percentage calculations in one place, with the working shown.