Temperature Converter
Convert a temperature between Celsius, Fahrenheit, Kelvin, Rankine and Réaumur. Negative values work, and the tool tells you if a value is below absolute zero.
Select two scales to see the formula.
This tool converts a temperature reading. To convert a temperature difference (for example “a rise of 10 °C”), use the Temperature Interval Converter, because the formulas are different.
Temperature Formula
Temperature scales do not all start at the same zero, so you cannot just multiply. This tool first changes your value into kelvin, then changes the kelvin value into the scale you chose. The key formulas are °F = °C × 9/5 + 32, °C = (°F − 32) × 5/9 and K = °C + 273.15. Nothing is rounded in between; only the final answer is shown to 10 significant digits.
What Is Temperature?
Temperature tells you how hot or cold something is. It measures the average energy of the tiny particles in a material. The SI unit is the kelvin (K).
This converter supports five everyday and scientific scales. Celsius (°C) is used in most of the world. It sets water to freeze at 0 °C and boil at 100 °C at normal air pressure. Fahrenheit (°F) is used mainly in the United States. Water freezes at 32 °F and boils at 212 °F. Kelvin (K) is the scientific scale. It starts at absolute zero, so it has no negative values. Rankine (°R) is the Fahrenheit-sized version of Kelvin and is used in some engineering work. Réaumur (°Ré) is an old scale that puts freezing at 0 and boiling at 80.
The list also has the triple point of water as a unit. This is the one exact temperature, 273.16 K (0.01 °C), where ice, liquid water and water vapor exist together. A value of 1 means exactly that temperature, and 2 means twice it on the kelvin scale.
Absolute zero is the lowest possible temperature: 0 K, −273.15 °C or −459.67 °F. Nothing can be colder, so the tool shows a clear message for any value below it.
Supported Units
This converter supports six temperature scales. Each one is linked to kelvin by a simple formula, shown below.
| Scale | Symbol | To kelvin | From kelvin |
|---|---|---|---|
| Kelvin | K | K = value | value = K |
| Celsius | °C | K = °C + 273.15 | °C = K − 273.15 |
| Fahrenheit | °F | K = (°F + 459.67) × 5/9 | °F = K × 9/5 − 459.67 |
| Rankine | °R | K = °R × 5/9 | °R = K × 9/5 |
| Réaumur | °Ré | K = °Ré × 5/4 + 273.15 | °Ré = (K − 273.15) × 4/5 |
| Triple point of water | T(tp) | K = value × 273.16 | value = K ÷ 273.16 |
How to Use the Temperature Converter
- Type the temperature in the value box. Negative numbers and decimals are fine, for example −12.5.
- Choose the From unit (the scale you have) and the To unit (the scale you want).
- The result appears instantly, or press Convert Now.
- Use Swap Units to reverse the conversion, Copy Result to copy the answer, open Show this temperature on all 6 scales to see every scale, and Clear to start again.
Worked example: 25 °C to °F
- Multiply by 9/5: 25 × 9/5 = 45.
- Add 32: 45 + 32 = 77 °F.
Worked example: 98.6 °F to °C
- Subtract 32: 98.6 − 32 = 66.6.
- Multiply by 5/9: 66.6 × 5/9 = 37 °C.
You can type a minus sign for temperatures below zero. Values below absolute zero are rejected.
Common Temperature Conversions
- Freezing point of water: 0 °C = 32 °F = 273.15 K.
- Boiling point of water (normal pressure): 100 °C = 212 °F = 373.15 K.
- Body temperature: 37 °C = 98.6 °F.
- Room temperature: 72 °F = 22.22222222 °C.
- The scales meet: −40 °C = -40 °F. This is the only point where Celsius and Fahrenheit agree.
- Absolute zero: 0 K = -273.15 °C = -459.67 °F = 0 °R.
- Oven: 180 °C = 356 °F; 350 °F = 176.6666667 °C.
- Réaumur: 80 °Ré = 100 °C.
Celsius to Other Temperature Scales
Quick reference for frequently used values
| °C | °F | K | °R |
|---|---|---|---|
| -40 | -40 | 233.15 | 419.67 |
| -20 | -4 | 253.15 | 455.67 |
| 0 | 32 | 273.15 | 491.67 |
| 10 | 50 | 283.15 | 509.67 |
| 20 | 68 | 293.15 | 527.67 |
| 37 | 98.6 | 310.15 | 558.27 |
| 100 | 212 | 373.15 | 671.67 |
| 200 | 392 | 473.15 | 851.67 |
Where and Why This Conversion Is Used
- Weather and travel: forecasts in °C or °F depending on the country.
- Cooking: oven and food-safety temperatures in recipes from other countries.
- Health: body temperature readings.
- Science and school: kelvin for physics and chemistry.
- Engineering: Rankine for some thermodynamic calculations.
Important Limitations
- The tool converts a temperature reading, not a temperature difference. A rise of 10 °C is a rise of 18 °F, not 50 °F. Use the Temperature Interval Converter for differences.
- Values below absolute zero are not accepted on any scale.
- Boiling and freezing points shown in examples are for water at normal air pressure. They change with pressure.
- Celsius is defined from kelvin (0 °C = 273.15 K). The Fahrenheit, Rankine and Réaumur scales are linked to it by exact formulas.
Important Differences Between Related Measurements
- Temperature vs heat: temperature shows how hot something is. Heat is energy. Use the Energy Converter for heat energy such as joules, calories and Btu.
- Temperature vs temperature interval: a reading is a point on a scale. An interval is a gap between two points and has no offset.