About the Celsius to Fahrenheit Converter
Convert Celsius to Fahrenheit, or Fahrenheit back to Celsius, with the exact formula and each step shown. The answer also comes in kelvin, the scientific scale, and a table covers everyday temperatures from the freezer to the oven.
Negative temperatures work as you'd expect, and anything colder than absolute zero is refused, because nothing can be colder than that.
How it works
The two scales have different zero points and different degree sizes. One Celsius degree is 1.8 Fahrenheit degrees, and water freezes at 0 °C, which is 32 °F. So to go from Celsius to Fahrenheit you multiply by 1.8 and add 32; to go back you subtract 32 and divide by 1.8.
Both numbers in the formula are exact by definition, so the only rounding is in the answer you see, to the number of decimal places you choose.
°F = °C × 1.8 + 32 (1.8 is the same as 9/5) °C = (°F − 32) ÷ 1.8 K = °C + 273.15
The scales meet at −40, where −40 °C and −40 °F are the same temperature.
Assumptions and limits
- Temperatures are absolute readings, such as the weather or an oven setting. A temperature difference converts without the 32: a rise of 10 °C is a rise of 18 °F.
- The lowest temperature accepted is absolute zero: −273.15 °C, −459.67 °F or 0 K.
Worked examples
Body temperature of 37 °C
37 × 1.8 = 66.6, and 66.6 + 32 = 98.6 °F, the figure often quoted for normal body temperature. A fever thermometer reading of 38 °C is 100.4 °F.
An oven set to 350 °F
350 − 32 = 318, and 318 ÷ 1.8 = 176.67 °C. Many recipes round this to 180 °C.
The 'double it and add 30' shortcut
For 20 °C the shortcut gives 70 °F against the exact 68 °F, 2 degrees too high. It is spot on at 10 °C, but the error grows by 0.2 °F for every degree you move away, so at 37 °C it is 5.4 °F off.
Everyday temperatures
Fahrenheit values rounded to 1 decimal place.
| What | Celsius | Fahrenheit |
|---|---|---|
| Typical freezer | −18 °C | −0.4 °F |
| Water freezes | 0 °C | 32 °F |
| Fridge | 4 °C | 39.2 °F |
| Room temperature | 20 °C | 68 °F |
| Hot summer day | 30 °C | 86 °F |
| Body temperature | 37 °C | 98.6 °F |
| Water boils (sea level) | 100 °C | 212 °F |
| Moderate oven | 180 °C | 356 °F |
| Hot oven | 220 °C | 428 °F |
How to use the Celsius to Fahrenheit Converter
- Type the temperature. Celsius by default; press Swap to start from Fahrenheit.
- Pick the decimal places. One decimal place suits weather and cooking.
- Read the result. Kelvin and the working are shown underneath.
Frequently asked questions
What is the formula for Celsius to Fahrenheit?
Multiply by 1.8 (or 9/5) and add 32. For 25 °C that is 25 × 1.8 = 45, plus 32 = 77 °F. To go the other way, subtract 32 first and then divide by 1.8.
Is there a quick way to convert in my head?
Double the Celsius figure and add 30. It is exact at 10 °C and within about 4 °F between −10 °C and 30 °C, but it drifts further outside that range, so use the calculator for cooking or medical readings.
At what temperature are Celsius and Fahrenheit equal?
At −40. Putting −40 into the formula gives −40 × 1.8 + 32 = −72 + 32 = −40, so −40 °C and −40 °F describe exactly the same temperature.
How do I convert a change in temperature?
Multiply by 1.8 and don't add 32. A difference has no zero point to shift, so a 5 °C rise is a 9 °F rise, not 41 °F. This page converts readings, not differences.
What is kelvin?
The SI unit of temperature, used in science. It starts at absolute zero, so 0 K is −273.15 °C, and a kelvin is the same size as a Celsius degree: add 273.15 to a Celsius reading to get kelvin.
Sources
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