How to use the celsius to fahrenheit converter
- Type the temperature value into the Temperature field.
- Select the conversion direction: Celsius to Fahrenheit or Fahrenheit to Celsius.
- Read the converted value, the formula used and the worked example below.
How the celsius to fahrenheit formula works
The formula to convert celsius to fahrenheit is F = C × 9/5 + 32. You multiply the Celsius value by 1.8 (which is 9 divided by 5) and then add 32. For example, to convert 25 °C: 25 × 1.8 = 45, then 45 + 32 = 77 °F.
To go from fahrenheit to celsius, reverse the steps: subtract 32 first, then multiply by 5/9. The formula is C = (F - 32) × 5/9. Converting 77 °F back: 77 - 32 = 45, then 45 × 5/9 = 25 °C.
Common temperature reference points
This table lists everyday and scientific reference temperatures in both scales. Use it to sanity-check your conversions.
| Description | Celsius (°C) | Fahrenheit (°F) |
|---|---|---|
| Absolute zero | -273.15 | -459.67 |
| Water freezes | 0 | 32 |
| Typical room temperature | 20 | 68 |
| Human body (average) | 37 | 98.6 |
| Water boils (sea level) | 100 | 212 |
| Oven baking (moderate) | 180 | 356 |
Why the two scales differ
The Celsius scale sets 0 at the freezing point of water and 100 at the boiling point under standard atmospheric pressure. Anders Celsius proposed it in 1742. The Fahrenheit scale, developed earlier by Daniel Gabriel Fahrenheit in 1724, places the freezing point of water at 32 and the boiling point at 212, giving 180 degrees between them instead of 100.
Because the degree sizes differ, one degree Celsius equals exactly 1.8 degrees Fahrenheit. The 32-degree offset accounts for the different zero points. This is why simply multiplying by a factor is not enough: you must also add or subtract 32 depending on the direction.
The crossover point: minus forty
There is exactly one temperature where the Celsius and Fahrenheit readings are identical: -40. Setting C equal to F in the conversion formula gives C = C × 9/5 + 32, which simplifies to -4C/5 = 32, so C = -40. At this extreme cold, which occurs in parts of Siberia, northern Canada and Antarctica during winter, you do not need to specify the scale because -40 °C and -40 °F are the same physical temperature.
Practical tips for quick mental conversion
For a rough c to f estimate without a calculator, double the Celsius value and add 30. For 20 °C: 20 × 2 + 30 = 70 °F (the exact answer is 68). This shortcut works well near typical weather temperatures but drifts further away from the range of 0 to 40 °C.
For f to c estimation, subtract 30 and halve the result. From 80 °F: (80 - 30) / 2 = 25 °C (exact is about 26.7). These tricks are handy when reading foreign weather forecasts or setting an oven dial that uses the other scale.
If you need to work with absolute temperatures in science, you may also need to convert to Kelvin. See the kelvin to celsius tool for that step.
Worked examples
Each result below was produced by the same code the tool runs, so you can check your own numbers against them.
| Example | Input | Result |
|---|---|---|
| Boiling point of water | Temperature: 100; Convert: c-to-f | Result: 212 °F; Formula: F = C × 9/5 + 32; Worked: 100 × 1.8 + 32 = 212 °F |
| Normal body temperature | Temperature: 98.6; Convert: f-to-c | Result: 37 °C; Formula: C = (F − 32) × 5/9; Worked: (98.6 − 32) × 5/9 = 37 °C |
| Room temperature | Temperature: 20; Convert: c-to-f | Result: 68 °F; Formula: F = C × 9/5 + 32; Worked: 20 × 1.8 + 32 = 68 °F |
| Freezing point | Temperature: 32; Convert: f-to-c | Result: 0 °C; Formula: C = (F − 32) × 5/9; Worked: (32 − 32) × 5/9 = 0 °C |
FAQ
What is the formula for celsius to fahrenheit?
Multiply the Celsius temperature by 9/5 (or 1.8) and add 32. Written out: F = C x 9/5 + 32.
How do I convert fahrenheit to celsius?
Subtract 32 from the Fahrenheit value, then multiply by 5/9. The formula is C = (F - 32) x 5/9.
At what temperature are Celsius and Fahrenheit equal?
They are equal at -40 degrees. Both -40 C and -40 F represent the same temperature.
Is 0 C the same as 0 F?
No. Zero degrees Celsius is 32 degrees Fahrenheit. Zero degrees Fahrenheit is approximately -17.78 degrees Celsius.
Which countries use Fahrenheit?
The United States, its territories, the Bahamas, Belize and the Cayman Islands use Fahrenheit for everyday temperatures. Most other countries use Celsius.
Why does the formula add 32?
The 32 accounts for the offset between the two scales' zero points. Water freezes at 0 C but at 32 F, so every Celsius-to-Fahrenheit conversion must shift by that amount after scaling.