Temperature Converter
Convert between Celsius, Fahrenheit, Kelvin, Rankine and Réaumur instantly. Real-time conversion, absolute-zero validation, no signup, works entirely in your browser.
Convert Temperature
What does this Temperature Converter do?
This free online temperature converter converts between any two temperature scales instantly. Whether you're cooking, doing science homework, checking the weather in a foreign country, or working on an engineering project, this tool gives you accurate results in real time.
It supports the three most common scales — Celsius, Fahrenheit, and Kelvin — plus the less common Rankine and Réaumur scales used in specific scientific and historical contexts. All conversions use internationally recognized, exact formulas.
The converter also validates your input against absolute zero — the lowest possible temperature — and shows a clear error if you enter a value below it. Everything runs locally in your browser. No server, no signup, no tracking.
How to use the Temperature Converter
- Enter a value: Type the temperature you want to convert in the "From" field.
- Pick your source scale: Select the scale you're converting from (Celsius, Fahrenheit, Kelvin, Rankine, or Réaumur).
- Pick your target scale: Select the scale you want to convert to.
- See the result instantly: The converted value appears in the "To" field and in the result box below — no button press needed.
- Use quick conversions: Click any of the preset buttons below to instantly convert common values like "0 °C → °F" or "100 °C → K".
- Swap scales: Click the swap button to reverse the conversion direction in one click.
- Copy the result: Use the "Copy Result" button to grab the converted value for use elsewhere.
Why use this Temperature Converter?
Real-time conversion
As you type, the result updates instantly. No button press needed, no waiting.
5 scales supported
Celsius, Fahrenheit, Kelvin, Rankine and Réaumur — covering scientific, everyday and historical use cases.
Absolute-zero validation
The converter checks your input against absolute zero and warns you if the value is physically impossible.
One-click swap
Swap the from and to scales instantly with a single click. No need to re-enter the value.
Copy & reset
Copy the result to your clipboard or reset the converter to its default state with one click.
Works offline
Once the page loads, the converter works without an internet connection. Perfect for travel or remote areas.
Temperature conversion formulas
Here are the exact formulas used by this converter. All conversions go through Celsius as the base unit, which ensures accuracy across every pair of scales.
| Conversion | Formula | Example |
|---|---|---|
| Celsius → Fahrenheit | °F = (°C × 9/5) + 32 | 25°C = 77°F |
| Fahrenheit → Celsius | °C = (°F − 32) × 5/9 | 77°F = 25°C |
| Celsius → Kelvin | K = °C + 273.15 | 25°C = 298.15 K |
| Kelvin → Celsius | °C = K − 273.15 | 298.15 K = 25°C |
| Fahrenheit → Kelvin | K = (°F + 459.67) × 5/9 | 77°F = 298.15 K |
| Kelvin → Fahrenheit | °F = (K × 9/5) − 459.67 | 298.15 K = 77°F |
| Celsius → Rankine | °R = (°C + 273.15) × 9/5 | 100°C = 671.67°R |
| Rankine → Celsius | °C = (°R − 491.67) × 5/9 | 671.67°R = 100°C |
| Celsius → Réaumur | °Ré = °C × 4/5 | 100°C = 80°Ré |
| Réaumur → Celsius | °C = °Ré × 5/4 | 80°Ré = 100°C |
Temperature scales compared
Different temperature scales were invented at different times for different purposes. Here's how they compare at some key reference points.
| Reference point | Celsius (°C) | Fahrenheit (°F) | Kelvin (K) | Rankine (°R) | Réaumur (°Ré) |
|---|---|---|---|---|---|
| Absolute zero | −273.15 | −459.67 | 0 | 0 | −218.52 |
| Water freezes | 0 | 32 | 273.15 | 491.67 | 0 |
| Room temperature | 20 | 68 | 293.15 | 527.67 | 16 |
| Body temperature | 37 | 98.6 | 310.15 | 558.27 | 29.6 |
| Water boils | 100 | 212 | 373.15 | 671.67 | 80 |
| Sun's surface | 5,500 | 9,932 | 5,773.15 | 10,391.67 | 4,400 |
About each scale
- Celsius (°C): The most widely used scale worldwide. Defined with 0°C at water's freezing point and 100°C at water's boiling point at sea level. Also called Centigrade.
- Fahrenheit (°F): Used primarily in the United States and a few other countries. Defined with 32°F at water's freezing point and 212°F at water's boiling point.
- Kelvin (K): The SI base unit of temperature. Starts at absolute zero (0 K) and uses the same degree size as Celsius. Used in science and engineering.
- Rankine (°R): An absolute scale like Kelvin, but uses the Fahrenheit degree size instead of the Celsius degree size. Used in some US engineering fields.
- Réaumur (°Ré): An obsolete scale that set 0°Ré at water's freezing point and 80°Ré at water's boiling point. Used historically in parts of Europe.
Common temperature conversion use cases
Cooking and baking
- Converting oven temperatures between Celsius and Fahrenheit for international recipes
- Checking meat doneness temperatures across different recipe sources
- Adjusting candy-making temperatures that require precise values
Science and academics
- Converting between Celsius and Kelvin for thermodynamic calculations
- Working with Rankine in US engineering textbooks
- Understanding historical scientific data recorded in Réaumur
Weather and travel
- Understanding weather forecasts in foreign countries
- Converting temperatures when traveling between countries that use different scales
- Reading climate data from international sources
Engineering and industry
- Converting process temperatures in manufacturing
- Working with HVAC specifications across regions
- Standardizing temperature readings across international teams