Summary: a temperature converter that is free and private
A temperature converter turns a reading from one scale into the others: Celsius (°C), Fahrenheit (°F), Kelvin (K), Rankine (°R) and Réaumur (°Ré). Type a number, press the scale it is in, and all five values appear at once, with the formula used. It runs in your browser, nothing is uploaded (you can check the Network tab in DevTools), and there is no sign-up.
The two conversions people need most are °F = °C × 9/5 + 32 and °C = (°F − 32) × 5/9. For example, 20 °C is 68 °F, and 98.6 °F is 37 °C. Results are shown to two decimal places.
Conversion formulas by input scale
| You enter | Formulas shown |
|---|---|
| Celsius (°C) | °F = °C × 9/5 + 32; K = °C + 273.15 |
| Fahrenheit (°F) | °C = (°F − 32) × 5/9; K = (°F − 32) × 5/9 + 273.15 |
| Kelvin (K) | °C = K − 273.15; °F = (K − 273.15) × 9/5 + 32 |
| Rankine (°R) | K = °R × 5/9; °F = °R − 459.67 |
| Réaumur (°Ré) | °C = °Ré × 5/4; °F = °Ré × 9/4 + 32 |
Table of Use: common temperature conversions
| Situation | You enter | Result |
|---|---|---|
| Room temperature | 20 °C | 68 °F, 293.15 K |
| Body temperature | 98.6 °F | 37 °C, 310.15 K |
| Hot day on a US forecast | 100 °F | 37.78 °C |
| Cool indoor temperature | 72 °F | 22.22 °C |
| Moderate oven, Celsius recipe | 180 °C | 356 °F |
| Moderate oven, US recipe | 350 °F | 176.67 °C |
| Freezer | 0 °F | −17.78 °C |
| Where the scales meet | −40 °C | −40 °F, 233.15 K |
| Absolute zero | 0 K | −273.15 °C, −459.67 °F |
Cooking by weight as well? The weight converter handles grams, ounces and pounds, and the volume calculator gives litres and gallons for a container.
Features
- Five scales in one converter, with every result updating as you type.
- Negative numbers, decimals, a decimal comma (36,6) and the Unicode minus sign (−5) pasted from documents are all accepted.
- A Conversion Formula box that shows the formulas for the scale you selected.
- A thermometer from −40 °C to 100 °C, with a note when your value is off that range.
- A Reference Points list: absolute zero, water freezing, room temperature (20 °C), body temperature (37 °C) and water boiling at sea level.
- A check for impossible input: anything below absolute zero is flagged rather than converted.
- A copy button that puts all five values on the clipboard as one line, such as 20°C = 68°F = 293.15 K = 527.67°R = 16°Ré.
For other quantities, the unit converter covers ten categories and the length converter handles distance and the area calculator surfaces. If the formulas above need more than a calculator, try the scientific calculator.
How to Use the Temperature Converter
- Press the Scale button for the unit you have: Celsius, Fahrenheit, Kelvin, Rankine or Réaumur. The label above the box changes to match.
- Type the number in Enter Temperature. It starts at 20.
- Read the other four values under Conversions.
- Check the Conversion Formula if you want to do it by hand, and compare with Reference Points for context.
- Press the copy button to take all five values with you.
Travelling abroad? Check the time difference with the time zone converter, and convert road speeds between km/h and mph with the speed calculator.
Who Can Use It
- Cooks and bakers following a recipe written in the other scale.
- Travellers and expats reading weather forecasts in unfamiliar units.
- Students in physics and chemistry, who need Kelvin and the working shown.
- Engineers and hobbyists who occasionally meet Rankine in older thermodynamics tables.
FAQs
How do I convert Celsius to Fahrenheit?
Multiply the Celsius temperature by 9/5 (1.8) and add 32: °F = °C × 9/5 + 32. So 20 °C is 20 × 1.8 + 32 = 68 °F, and body temperature of 37 °C is 98.6 °F. For a rough mental answer, double the Celsius value and add 30, which gives 70 °F for 20 °C.
How do I convert Fahrenheit to Celsius?
Subtract 32 from the Fahrenheit temperature, then multiply by 5/9: °C = (°F − 32) × 5/9. For example, 98.6 °F gives (98.6 − 32) × 5/9 = 37 °C, and a 350 °F oven is 176.67 °C. Select Fahrenheit on the converter, type the number, and the Celsius value appears straight away.
At what temperature are Celsius and Fahrenheit the same?
At −40. Set °C equal to °C × 9/5 + 32 and the only solution is −40, so −40 °C is exactly −40 °F. It is the one point where the two scales cross, which is why it is a handy check that a conversion formula has been applied the right way round.
How do I convert Celsius to Kelvin?
Add 273.15 to the Celsius temperature: K = °C + 273.15. So 0 °C is 273.15 K and 100 °C is 373.15 K. Kelvin is written without a degree sign, and it has no negative values because 0 K is absolute zero. A change of 1 K is the same size as a change of 1 °C.
What is 180 °C in Fahrenheit for an oven?
Exactly 356 °F. Recipes usually round it to 350 °F, and likewise 200 °C is 392 °F, usually written 400 °F, and 160 °C is 320 °F. A few degrees rarely matter for baking, but if a recipe is precise, type the Celsius value into the converter and use the exact figure.
Why does the converter say my temperature is below absolute zero?
Absolute zero is 0 K, −273.15 °C or −459.67 °F, the lowest temperature physically possible. If the number you typed converts to something colder, the converter shows an error instead of an impossible result. Check the selected scale: −300 is impossible in Celsius but a valid Fahrenheit reading.
What are the Rankine and Réaumur scales?
Rankine is an absolute scale with Fahrenheit-sized degrees, so 0 °R is absolute zero and °R = °F + 459.67. Réaumur, once common in Europe, puts water’s freezing point at 0 °Ré and its boiling point at 80 °Ré, so °Ré = °C × 4/5. Both are rare today, but the converter handles them.