Celsius and Fahrenheit are the two most common scales used to measure temperature in the world. While most of the world uses the Celsius scale as part of the metric system, the United States, along with a few other countries, continues to use Fahrenheit. This difference can make everything from reading international weather reports to following a recipe from another country a bit confusing. Our Temperature Converter is a dynamic, two-way tool designed to make these conversions instant and effortless, allowing you to seamlessly translate temperatures between Celsius (°C) and Fahrenheit (°F).
How to Use the Temperature Converter
Our converter is designed for instant, two-way conversions with no need to click a button:
- To Convert from Celsius to Fahrenheit: Simply start typing a temperature in the "Celsius (°C)" field. The equivalent temperature in Fahrenheit will appear in the other field automatically.
- To Convert from Fahrenheit to Celsius: Start typing a temperature in the "Fahrenheit (°F)" field, and the equivalent Celsius temperature will appear instantly.
The Formulas for Conversion
The relationship between the Celsius and Fahrenheit scales is linear, meaning it can be described by a simple algebraic formula. However, the scales have different starting points (where water freezes) and different interval sizes, which is why a direct conversion is necessary.
Celsius to Fahrenheit
To convert a temperature from Celsius to Fahrenheit, you first multiply the Celsius temperature by 9/5 (or 1.8), and then you add 32.
°F = (°C × 9/5) + 32
Example: Let's convert a pleasant day of 20°C to Fahrenheit.
(20 × 9/5) + 32 = (20 × 1.8) + 32 = 36 + 32 = 68°F.
Fahrenheit to Celsius
To convert a temperature from Fahrenheit to Celsius, you do the reverse operations. First, you subtract 32 from the Fahrenheit temperature, and then you multiply the result by 5/9.
°C = (°F - 32) × 5/9
Example: Let's convert a hot summer day of 86°F to Celsius.
(86 - 32) × 5/9 = 54 × 5/9 = 30°C.
The Origins of the Scales
The scales we use today have fascinating histories rooted in the scientific advancements of the 18th century.
- The Fahrenheit Scale: Developed by the German physicist Daniel Gabriel Fahrenheit in 1724, this was one of the first standardized temperature scales. He based his scale on three fixed points: 0°F was the freezing point of a brine solution, 32°F was the freezing point of pure water, and he initially set 96°F as the temperature of the human body (though this was later refined).
- The Celsius Scale: Developed by the Swedish astronomer Anders Celsius in 1742, this scale is based on the properties of water. Originally, Celsius set 0°C as the boiling point of water and 100°C as its freezing point. A year later, this was inverted to the modern standard we use today, where 0°C is the freezing point and 100°C is the boiling point at standard atmospheric pressure. This logical, base-100 structure is why it was adopted as part of the metric system.
The Kelvin Scale: The Absolute Temperature
In scientific work, a third scale is often used: the Kelvin (K) scale. The Kelvin scale is an absolute temperature scale, meaning its zero point, 0 K, is "absolute zero"—the theoretical temperature at which all atomic motion ceases. A change of one Kelvin is exactly the same as a change of one degree Celsius, which makes converting between them very simple:
K = °C + 273.15
Because it's an absolute scale, temperatures in Kelvin are not referred to in "degrees."
Frequently Asked Questions
Is there a temperature where Celsius and Fahrenheit are the same?
Yes. The two scales meet at one point: -40. So, -40°C is equal to -40°F. It is the only temperature at which the two scales agree.
Why does the U.S. still use Fahrenheit?
The continued use of Fahrenheit in the United States is largely due to historical precedent and cultural inertia. The system was established in the U.S. long before the metric system and Celsius were widely adopted internationally. While there have been efforts to switch, the enormous cost and cultural familiarity have made a complete transition difficult.
What is a good way to mentally approximate a Celsius temperature in Fahrenheit?
A quick and easy mental shortcut is to double the Celsius temperature and then add 30. For example, for 15°C: double it to get 30, then add 30 to get 60°F. The actual answer is 59°F, so this method provides a very close estimate for typical weather temperatures.