What this converter does
This tool changes a temperature from one scale to another. Pick Fahrenheit, Celsius or Kelvin, type a number, and the other two scales appear right away. Fahrenheit is the everyday scale in the United States. Celsius is used in most other countries and in science. Kelvin is the scientific scale that starts at absolute zero, the coldest temperature that is physically possible.
People use a Fahrenheit to Celsius converter for many reasons: reading a recipe from another country, checking a weather forecast while traveling, following a lab procedure, or making sense of a thermometer reading. The converter gives the answer and shows the formula, so you can also learn how to do it by hand.
How to use it
- Type the temperature in the box. Negative numbers are fine, for example −10.
- Choose the unit you are converting from: Fahrenheit, Celsius or Kelvin.
- Choose how many decimal places you want. One decimal place is enough for most uses.
- Read the results. The first result is shown in large type, and the second one appears below it.
If you enter a value below absolute zero, the tool shows a message instead of a result, because no object can be colder than that.
Temperature conversion formulas
All three scales are linked by simple formulas. They come from two facts: water freezes at 32 °F and 0 °C, and it boils at 212 °F and 100 °C at sea level. That means 180 Fahrenheit degrees cover the same range as 100 Celsius degrees, a ratio of 9 to 5.
°C = (°F − 32) × 5 ÷ 9
°F = °C × 9 ÷ 5 + 32
K = °C + 273.15
°C = K − 273.15
The National Institute of Standards and Technology (NIST) lists these relations in its guide to the International System of Units. The Kelvin scale uses the same size of degree as Celsius, so converting between them is only a shift of 273.15. Kelvin is written without a degree sign: 300 K, not 300 °K.
A quick mental shortcut
For a rough Celsius answer, subtract 30 from the Fahrenheit number and cut it in half. For 70 °F, that gives (70 − 30) ÷ 2 = 20 °C. The exact answer is 21.1 °C, so the shortcut is close for everyday weather but not good enough for cooking precision or science.
Worked examples
| Starting value | Calculation | Result |
|---|---|---|
| 32 °F | (32 − 32) × 5 ÷ 9 | 0 °C (freezing point of water) |
| 50 °F | (50 − 32) × 5 ÷ 9 | 10 °C |
| 68 °F | (68 − 32) × 5 ÷ 9 | 20 °C |
| 98.6 °F | (98.6 − 32) × 5 ÷ 9 | 37 °C |
| 100 °F | (100 − 32) × 5 ÷ 9 | 37.8 °C |
| 350 °F | (350 − 32) × 5 ÷ 9 | 176.7 °C |
| 212 °F | (212 − 32) × 5 ÷ 9 | 100 °C (boiling point at sea level) |
| 20 °C | 20 × 9 ÷ 5 + 32 | 68 °F |
| 300 K | 300 − 273.15 | 26.85 °C, or 80.33 °F |
The point −40 is special. At −40 °C the temperature is also −40 °F, so the two scales meet there.
Where each scale is used
The Fahrenheit scale is the everyday standard in the United States and a few other places, so weather reports, ovens and home thermostats there use it. Almost everywhere else, people use Celsius for the same things. Scientists around the world use Celsius and Kelvin, because the numbers are easy to combine with other metric units.
That is why a recipe from a British or Australian website may say 180 °C while an American oven dial shows 350 °F. A fever reading of 38 °C sounds unfamiliar to many Americans, but it is 100.4 °F. Knowing both scales helps when you travel, cook, study science or read international news.
Rounding tips
For weather and cooking, whole degrees are plenty. For science homework, follow the number of significant figures your teacher asks for. Pick zero or one decimal place in the converter and the answer is rounded only at the very end, so rounding errors do not build up.
Frequently asked questions
- How do I convert Fahrenheit to Celsius?
- Subtract 32 from the Fahrenheit temperature, then multiply the result by 5 and divide by 9. For example, 86 °F gives (86 − 32) × 5 ÷ 9 = 30 °C.
- How do I convert Celsius to Fahrenheit?
- Multiply the Celsius temperature by 9, divide by 5, and add 32. For example, 25 °C gives 25 × 9 ÷ 5 + 32 = 77 °F.
- What is 350 °F in Celsius?
- 350 °F is 176.7 °C when rounded to one decimal place. Many ovens in other countries are set to 180 °C, which is about 356 °F.
- Is the formula exact or an approximation?
- The relation between Fahrenheit and Celsius is exact. Only the displayed result is rounded, to the number of decimal places you choose.
- What is the lowest possible temperature?
- Absolute zero: 0 K, which is −273.15 °C or −459.67 °F. The converter rejects anything lower.
Things to keep in mind
A temperature difference converts differently from a temperature reading. A rise of 10 Celsius degrees equals a rise of 18 Fahrenheit degrees, with no 32 added. This converter is for readings on a thermometer. Also, a household thermometer is only accurate to a degree or so, so extra decimal places do not make a measurement more reliable. For medical, laboratory or food-safety decisions, follow the instructions from the relevant professional or official guidance.