Why there are three temperature scales in common use
Celsius, Fahrenheit, and Kelvin all measure the same physical property, thermal energy, but were defined using different reference points for historical reasons. Celsius sets 0° and 100° at water's freezing and boiling points, making it intuitive for everyday weather and cooking contexts. Fahrenheit uses a finer-grained scale historically calibrated against different reference points, and remains the standard in a small number of countries, notably the United States. Kelvin starts at absolute zero, the theoretical point where molecular motion stops entirely, which makes it the scale scientists use, since it has no negative values and directly corresponds to thermal energy.
None of the three is "more correct" than the others; they're just different units for the same underlying quantity, similar to how a distance can be expressed in miles or kilometers.
How to convert between temperature scales
- Enter a temperature value in any of the three fields. Celsius, Fahrenheit, or Kelvin.
- The other two update automatically to show the equivalent temperature.
- There's no need to remember the conversion formulas; the tool calculates them instantly as you type.
This is especially useful when working with recipes, weather data, or scientific figures sourced from a country or context that uses a different scale than the one you're used to.
Common reference points worth knowing
Water freezes at 0°C, 32°F, and 273.15K, and boils at 100°C, 212°F, and 373.15K at standard atmospheric pressure. Normal human body temperature is roughly 37°C or 98.6°F. A comfortable room temperature is typically cited as somewhere around 20-22°C, or 68-72°F.
These reference points are useful for a quick sanity check on a conversion. If a converted value seems wildly off from what you'd expect for the context (a "hot day" converting to a temperature that seems too cold, for instance), it's worth double-checking which direction the conversion was meant to go.