This switches a temperature between Celsius, Fahrenheit, and Kelvin, the three scales you'll run into in weather reports, recipes, and science. Because the scales don't share a simple ratio, converting by hand is an easy way to get it wrong, and this applies the correct formula instantly, giving you an exact answer instead of a rounded guess.
How to use it
- Enter the temperature you want to convert.
- Select the scale you're converting from.
- Select the scale you want it in.
- Read the converted temperature.
- Change the value and watch it update instantly.
When it helps
- Converting an oven temperature from Fahrenheit to Celsius for a recipe from another country.
- Understanding a weather forecast in an unfamiliar scale while traveling.
- Converting lab measurements to and from Kelvin for a calculation.
- Checking a body temperature reading between Celsius and Fahrenheit.
- Converting an industrial temperature spec between regional standards.
Good to know
- Water freezes at 0 Celsius, 32 Fahrenheit, and 273.15 Kelvin, and boils at 100, 212, and 373.15.
- A rough mental shortcut for Celsius to Fahrenheit is to double it and add 30, though this tool gives you the exact number.
- Kelvin doesn't go negative in normal use, since zero Kelvin is absolute zero, the coldest anything can physically get.
- When following a recipe from another country, convert the exact oven temperature given rather than relying on a rough rule of thumb, since baking depends on precise temperatures.
- If you're converting a range of temperatures, like a weather forecast's high and low, convert both ends separately rather than trying to convert the difference between them.
Mental shortcuts
To go from Celsius to Fahrenheit roughly, double the number and add 30. To go back, subtract 30 and halve it. The shortcut is within a couple of degrees for everyday weather temperatures.
Questions
Why does science use Kelvin instead of Celsius?
Kelvin starts at absolute zero, where molecular motion theoretically stops, which makes it more convenient for physics and chemistry calculations involving ratios.
What's the exact formula between Celsius and Fahrenheit?
Fahrenheit equals Celsius times nine fifths, plus 32. Going the other way, Celsius equals Fahrenheit minus 32, times five ninths.
Can temperature be negative?
Celsius and Fahrenheit both go negative below their freezing points. Kelvin can't, since zero represents absolute zero.
Why does a Celsius forecast feel so different from Fahrenheit?
The two scales use different sized degree increments, so the same real change in temperature looks like a bigger swing in Fahrenheit.
Is there a temperature that reads the same on both scales?
Yes, negative 40 is the one point where Celsius and Fahrenheit show the same number, since that's exactly where the two formulas cross.
Why do some countries use Fahrenheit while most use Celsius?
It largely comes down to historical adoption. Celsius became the international scientific and everyday standard almost everywhere, while a handful of countries, including the United States, kept using Fahrenheit for everyday purposes.