Temperature converter for Celsius, Fahrenheit and Kelvin. Convert °C to °F for weather, fever or cooking, with absolute zero checks, free in your browser.

What is the Temperature Converter?

A thermometer at home may read in Fahrenheit, the weather app in Celsius and a science textbook in kelvin. This temperature converter moves a reading between all three scales in one step. Enter the temperature, choose the scale it is in and the scale you want, and you get the converted value instantly. It is handy for checking a fever, following a foreign recipe or solving a physics problem.

The tool uses the exact relationships K = °C + 273.15 and °C = (°F − 32) × 5/9. Negative temperatures in Celsius and Fahrenheit are accepted, so winter readings or freezer settings convert correctly. Values below absolute zero are rejected with a clear message, since nothing can be colder. Note that it converts actual temperatures, not temperature differences, and the result is shown as a number followed by the scale name, such as 98.6 Fahrenheit.

How to use the Temperature Converter

Enter the reading in the Temperature field, for example 98.6 or -18.
Choose its scale from From scale: Celsius, Fahrenheit or Kelvin.
Choose the scale you want from To scale.
Press Calculate to see the converted temperature, followed by the name of the target scale.
Copy the result or press Reset to convert another value.

Features

Converts between Celsius, Fahrenheit and Kelvin
Exact formulas using 273.15 and the 5/9 factor
Accepts negative and decimal temperatures
Rejects values below absolute zero
Results to up to 4 decimals, followed by the scale name

Why use this temperature converter

Understand fever readings from any thermometer
Follow recipes and oven settings from abroad
Check homework and lab answers in kelvin
Instant and private, no download needed

Formula used

K=C+273.15; C=(F−32)×5/9; convert through kelvin and reject values below 0 K.

Examples

Body temperature in Fahrenheit

Input: Temperature: 37, From scale: Celsius, To scale: Fahrenheit

Result: 98.6 Fahrenheit The commonly quoted normal body temperature of 37 °C equals 98.6 °F.

Where the scales meet

Input: Temperature: -40, From scale: Celsius, To scale: Fahrenheit

Result: -40 Fahrenheit Minus 40 is the one temperature that reads the same in Celsius and Fahrenheit.

Kelvin to Celsius

Input: Temperature: 300, From scale: Kelvin, To scale: Celsius

Result: 26.85 Celsius Subtracting 273.15 from 300 K gives about 27 °C, a warm room.

Results are estimates for general information, not financial, medical, legal, tax, or property advice. Confirm important figures with the relevant institution or a qualified professional.

Temperature Converter: frequently asked questions

How do I convert Celsius to Fahrenheit by hand?

Multiply the Celsius value by 9/5, or 1.8, and add 32. For example, 30 °C × 1.8 = 54, plus 32 gives 86 °F. To go back, subtract 32 from Fahrenheit and multiply by 5/9. The converter applies these exact formulas, so you can use it to check your working.

Is 100 °F a fever?

100 °F is about 37.8 °C, which is above the commonly quoted normal of 37 °C (98.6 °F), and many doctors consider 100.4 °F (38 °C) or higher a fever. This converter only changes units and is not medical advice. If you are worried about a high or persistent temperature, contact a doctor.

Why does it reject some negative numbers?

Negative Celsius and Fahrenheit values are fine as long as they are above absolute zero, the lowest possible temperature: 0 K, −273.15 °C or −459.67 °F. Anything colder is physically impossible, so the tool shows an error instead of a result. Kelvin values themselves cannot be negative.

Can I convert a temperature change, like a rise of 10 degrees?

No. The tool converts actual readings, which involves the 32-degree offset between Celsius and Fahrenheit. A change of 10 °C is a change of 18 °F, but converting 10 °C as a reading gives 50 °F. For differences, multiply by 1.8 yourself instead of using the converter.

Why is kelvin written without a degree sign?

Kelvin is an absolute scale that starts at absolute zero, and the official SI unit is simply the kelvin, written K, for example 273.15 K. Celsius and Fahrenheit use degrees. The converter writes the scale name after the number, such as 273.15 Kelvin or 32 Fahrenheit, so use the symbols K, °C or °F when you need the short form in your notes.