How the Temperature Converter Works
Temperature is measured on different scales around the world. Most countries use Celsius, the United States uses Fahrenheit for daily life, and scientists use Kelvin. The Temperature Converter changes a temperature from one scale into another, so you can read a weather report from another country, set an oven, or check a fever.
What you enter
- The temperature: a number, which can have decimals and can be below zero.
- The scale you have (From): Celsius (°C), Fahrenheit (°F) or Kelvin (K).
- The scale you want (To): any of the same scales.
The formulas
The scales start at different points and have steps of different sizes, so a temperature is not changed by simple multiplying. These are the exact formulas:
| To change | Formula |
|---|---|
| °C to °F | °F = °C x 9/5 + 32 |
| °F to °C | °C = (°F − 32) x 5/9 |
| °C to K | K = °C + 273.15 |
| K to °C | °C = K − 273.15 |
| °F to K | K = (°F − 32) x 5/9 + 273.15 |
| K to °F | °F = (K − 273.15) x 9/5 + 32 |
The converter changes your temperature into Kelvin first, and then into the scale you chose. The answer is shown with 2 decimal places.
A worked example
You want to change 25°C into Fahrenheit and Kelvin.
| Step | Value |
|---|---|
| 25 x 9/5 | 45 |
| 45 + 32 | 77 °F |
| 25 + 273.15 | 298.15 K |
Going back is just as simple. A body temperature of 98.6°F is (98.6 − 32) x 5/9 = 66.6 x 5/9 = 37°C.
Common temperatures
| Point | °C | °F | K |
|---|---|---|---|
| Absolute zero | −273.15 | −459.67 | 0 |
| Water freezes | 0 | 32 | 273.15 |
| Room | 20 | 68 | 293.15 |
| Body | 37 | 98.6 | 310.15 |
| Water boils | 100 | 212 | 373.15 |
Celsius to Fahrenheit
| °C | °F |
|---|---|
| −40 | −40 |
| −20 | −4 |
| 0 | 32 |
| 10 | 50 |
| 20 | 68 |
| 25 | 77 |
| 30 | 86 |
| 37 | 98.6 |
| 100 | 212 |
Chart: four points in Celsius
The longer the bar, the higher the number. Blue is cold and red is hot.
Water freezes 0°C ▏ Room 20°C ████████ Body 37°C ███████████████ Water boils 100°C ████████████████████████████████████████
Chart: the same four points in Fahrenheit
These are the same temperatures, but the numbers are different. Zero Celsius is 32 on the Fahrenheit scale, so the first bar is not empty.
Water freezes 32°F ██████ Room 68°F █████████████ Body 98.6°F ███████████████████ Water boils 212°F ████████████████████████████████████████
Doing it by hand
- Celsius to Fahrenheit: multiply by 1.8 and add 32. So 30°C is 54 + 32 = 86°F.
- Fahrenheit to Celsius: subtract 32 and divide by 1.8. So 68°F is 36 / 1.8 = 20°C.
- Celsius to Kelvin: add 273.15. For rough work, add 273.
A quick estimate: to go from Celsius to Fahrenheit, double the number and add 30. For 25°C that gives 80°F, and the exact answer is 77°F. To go back, subtract 30 and halve it. For 77°F that gives 23.5°C, and the exact answer is 25°C. The estimate is good for ordinary weather, but not for cooking or science.
Where these conversions are used
- Weather and travel: a forecast of 30°C is 86°F.
- Cooking: an oven at 180°C is 356°F, and 350°F is 176.7°C.
- Health: a fever of 38°C is 100.4°F.
- Science and school: Kelvin is used in physics and chemistry, and gas law problems need it.
- Home and cars: thermostats, freezers and engine gauges.
Tips
- Kelvin has no degree sign. You write 298.15 K, and not 298.15°K.
- A change is not the same as a temperature. A rise of 1°C is a rise of 1 K, and it is a rise of 1.8°F. The "+32" part is used only for a temperature on the scale, and not for a difference.
- −40 is the same on both scales. It is −40°C and −40°F.
- There is a lowest temperature. Nothing can be colder than absolute zero (0 K, −273.15°C or −459.67°F).
What this converter does not include
- Rankine, Réaumur and other old scales.
- Temperature differences. This tool converts a temperature on the scale.
- Wind chill and heat index. Use a wind chill or heat index calculator for those.
This tool gives an estimate for general information only. For medicine, food safety or science that needs a precise reading, use a calibrated thermometer and follow the official guidance.