The three temperature scales
Celsius (°C) is used by most of the world and science, with water freezing at 0° and boiling at 100°. Fahrenheit (°F) is used mainly in the United States, with water freezing at 32° and boiling at 212°. Kelvin (K) is the scientific standard for absolute temperature — it uses the same size "degree" as Celsius but starts at absolute zero (−273.15°C), the coldest temperature theoretically possible, so Kelvin values are never negative.
Frequently asked questions
Why doesn't Kelvin go below zero?
Zero Kelvin represents absolute zero, the point at which particles have minimal thermal motion — there's no colder temperature to measure, so negative Kelvin values don't occur in normal use.
Which countries still use Fahrenheit?
The United States is the main country that uses Fahrenheit for everyday weather and cooking temperatures; nearly everywhere else has standardized on Celsius.
How do I convert a body temperature reading?
Enter the reading into whichever field matches your thermometer — for example, a normal 37°C reading converts to 98.6°F, which the calculator will show instantly in the other two fields.