Free converter

Temperature Converter

To convert Celsius to Fahrenheit, multiply by 9/5 and add 32. To convert Fahrenheit to Celsius, subtract 32 and multiply by 5/9.

By iToolsLab Editorial TeamUpdated 14 October 2026How we build tools

What is temperature converter?

Temperature scales are used differently around the world. Most countries use Celsius, the United States uses Fahrenheit for daily life, and scientists use Kelvin.

This converter shows all three at once, so a weather forecast, an oven setting or a lab value is easy to understand in the scale you know.

How to use the temperature converter

  1. Enter the temperature.
  2. Choose the unit it is in.
  3. Read the matching values in Celsius, Fahrenheit and Kelvin.

How the temperature converter works

Celsius to Fahrenheit: F = C x 9/5 + 32. Fahrenheit to Celsius: C = (F minus 32) x 5/9. Celsius to Kelvin: K = C + 273.15. Values below absolute zero (minus 273.15 C) are rejected.

Worked example

25 C is 77 F and 298.15 K. Water freezes at 0 C or 32 F and boils at 100 C or 212 F at sea level. Normal body temperature is about 37 C or 98.6 F.

Common uses of the temperature converter

  • Reading an oven setting from an overseas recipe.
  • Understanding a weather forecast when you travel.
  • Checking body temperature or a fever reading.
  • Converting lab and science homework values.
  • Setting a thermostat or aquarium heater.

Tips and common mistakes

A quick mental estimate from Celsius to Fahrenheit is to double the number and add 30.

Oven recipes often list both scales. Check which one your oven uses before you set it.

Background: what to know before you rely on it

Daniel Fahrenheit proposed his scale in the early 1700s, and Anders Celsius followed in 1742 with a scale based on the freezing and boiling points of water. The Kelvin scale, named after Lord Kelvin, starts at absolute zero and is used in science because it has no negative values. A change of one degree is the same size on the Celsius and Kelvin scales, which makes Kelvin easy to use. The Fahrenheit degree is smaller, so a rise of 9 degrees Fahrenheit equals a rise of 5 degrees Celsius. The two scales meet at minus 40, which is a handy fact for quizzes.

Private, free and fast

This tool runs entirely in your browser. What you type or choose is not uploaded to a server and is not saved after you close the page, which keeps it fast and private. It is free to use as often as you like. See more in all converters, or browse the full list of tools.

Frequently asked questions

How do I convert Celsius to Fahrenheit?

Multiply by 1.8 and add 32.

What is 0 Kelvin?

Absolute zero, which is minus 273.15 C or minus 459.67 F.

At what temperature are Celsius and Fahrenheit equal?

At minus 40.

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Results are for information and education. For legal, financial, medical or security decisions, check with a qualified professional. Check critical conversions with an official source.