CALCULATORS & CONVERTERS
Temperature Converter — Celsius, Fahrenheit, Kelvin
Convert temperature between Celsius, Fahrenheit, and Kelvin instantly. Shows the real conversion formulas, runs in your browser, no signup.
Your files never leave your device.
100°C = 212°F
Convert a temperature between Celsius, Fahrenheit, and Kelvin — for a US recipe in Fahrenheit, a European forecast in Celsius, or a physics problem in Kelvin.
Unlike length or weight, the temperature scales do not just differ by a factor: they have different zero points, so a conversion has to shift as well as scale. The table below is the exact set of formulas this tool applies.
The conversion formulas
| Conversion | Formula | Example |
|---|---|---|
| Celsius → Fahrenheit | °F = °C × 9/5 + 32 | 20 °C = 68 °F |
| Fahrenheit → Celsius | °C = (°F − 32) × 5/9 | 212 °F = 100 °C |
| Celsius → Kelvin | K = °C + 273.15 | 25 °C = 298.15 K |
| Kelvin → Celsius | °C = K − 273.15 | 0 K = −273.15 °C |
−40 °C equals −40 °F — the single point where the two scales meet, and a quick sanity check that a converter is working.
Frequently asked questions
- How do I convert Celsius to Fahrenheit in my head?
- Multiply by 1.8 and add 32. For a rough estimate, double the Celsius and add 30 — close enough for weather, though the exact formula (×9/5 + 32) is what the tool uses.
- Why can't Kelvin be negative?
- Kelvin starts at absolute zero (0 K = −273.15 °C), the lowest temperature physically possible, so a valid Kelvin value is never negative. A negative result means the input was below absolute zero and is unphysical.
- Does it use the same degree size for Celsius and Kelvin?
- Yes. Kelvin and Celsius degrees are the same size; only the zero point differs (0 °C = 273.15 K). Fahrenheit degrees are smaller, which is why its formula also scales by 9/5.