Fahrenheit to Celsius Converter
Step outside in Phoenix, glance at your phone, and it says 104. Step off a plane in Paris and the same kind of heat reads 40.
Both are the same hot afternoon, and the gap between the numbers is the Fahrenheit-to-Celsius conversion. This page shows you how it works, why the numbers look so different, and how to do it in your head when you do not have a converter handy.
Quick answer: subtract 32 from the Fahrenheit value, then multiply by 5/9 (about 0.5556). So 212 °F becomes 100 °C and 68 °F becomes 20 °C.
The Fahrenheit to Celsius formula
The conversion is a two-step recipe: remove the 32-degree head start that the Fahrenheit scale has, then rescale the degrees. Written out:
The same relationship is often written as a proportion, which makes the logic easier to see: TC / 5 = (TF − 32) / 9. Both forms give identical answers.
Why 32 and why 5/9?
The two scales are anchored to the same two physical events but number them differently. Water freezes at 0 °C and 32 °F, and boils at 100 °C and 212 °F (at standard atmospheric pressure). The Celsius scale splits the span between those points into 100 equal degrees, while the Fahrenheit scale splits it into 180 (Britannica).
That is where the factor comes from: 100 ÷ 180 reduces to 5/9, so one Fahrenheit degree is a smaller step than one Celsius degree. The subtraction of 32 exists because Fahrenheit already reads 32 at the moment Celsius reads zero.
How to convert Fahrenheit to Celsius, step by step
- Write down the Fahrenheit temperature.
- Subtract 32.
- Multiply the result by 5.
- Divide by 9.
- Round to the precision you need and add the °C symbol.
Example 1: boiling water
- Start with 212 °F.
- Subtract 32: 212 − 32 = 180.
- Multiply by 5: 180 × 5 = 900.
- Divide by 9: 900 ÷ 9 = 100.
212 °F = 100 °C
Example 2: a mild room
- Start with 68 °F.
- 68 − 32 = 36.
- 36 × 5 = 180.
- 180 ÷ 9 = 20.
68 °F = 20 °C
Example 3: a temperature that is not tidy
- Start with 98.6 °F, the traditional figure quoted for average human body temperature.
- 98.6 − 32 = 66.6.
- 66.6 × 5 = 333.
- 333 ÷ 9 = 37.
98.6 °F = 37 °C
Fahrenheit to Celsius conversion table
Bookmark this reference for the values you will use most. Every row was computed with the formula above and rounded to two decimals.
| Fahrenheit (°F) | Celsius (°C) |
|---|---|
| -40 °F | -40 °C |
| 0 °F | -17.78 °C |
| 14 °F | -10 °C |
| 32 °F | 0 °C |
| 50 °F | 10 °C |
| 68 °F | 20 °C |
| 77 °F | 25 °C |
| 86 °F | 30 °C |
| 98.6 °F | 37 °C |
| 100 °F | 37.78 °C |
| 212 °F | 100 °C |
| 350 °F | 176.67 °C |
| 400 °F | 204.44 °C |
The mental shortcut, and how wrong it gets
When you only need a feel for the weather, subtract 30 and halve the result. It is quick, but it is an approximation: the real factor is 0.5556, not 0.5, and the 32 is rounded to 30. At 70 °F the shortcut gives 20 °C while the exact answer is 21.1 °C.
At 90 °F it gives 30 °C against an exact 32.2 °C. The error grows as temperatures climb, so use the exact formula for cooking, lab work, engineering or anything you will write down.
Where you will meet this conversion
- Weather and travel: the United States uses Fahrenheit for everyday temperatures, while most other countries use Celsius (Britannica), so forecasts and hotel thermostats rarely match across borders.
- Cooking: American recipes give oven settings in °F. A 350 °F oven is 176.7 °C, which most Celsius ovens round to 180 °C.
- Science and engineering: technical work is done in Celsius or Kelvin, so a Fahrenheit reading from a US datasheet usually has to be converted first.
Common mistakes to avoid
- Multiplying before subtracting. Always subtract 32 first. Doing 5/9 first and then subtracting 32 gives the wrong answer.
- Using 9/5 instead of 5/9. 9/5 goes the other way, from Celsius to Fahrenheit.
- Applying the formula to a temperature difference. A change of 18 °F is a change of 10 °C, with no 32 involved. See the temperature difference calculator.
Good to know: −40 is the one temperature that reads the same on both scales, because −40 °F = −40 °C (Omni Calculator). It makes a handy sanity check for any converter.
Related converters
Need the opposite direction? Try Celsius to Fahrenheit. For scientific work, Fahrenheit to Kelvin and Kelvin to Celsius continue the chain, and absolute temperature shows all the scales side by side.
One degree versus one degree
A useful way to feel the difference between the scales is to compare the size of a single degree. One Celsius degree is 1.8 Fahrenheit degrees, which means one Fahrenheit degree is only 5/9 (about 0.56) of a Celsius degree. Fahrenheit therefore offers finer steps: the jump from 70 °F to 71 °F is smaller than the jump from 21 °C to 22 °C.
That is also why the sign of the answer can change meaning. A 9 °F fall in temperature is a 5 °C fall, and a reading below 32 °F always means below freezing for water.
Oven temperatures from Fahrenheit to Celsius
Recipes are the most common reason to convert Fahrenheit to Celsius, so here are the exact values for typical oven settings. Most Celsius ovens use round numbers, so you will usually pick the nearest 5 or 10 degrees on your dial.
| Oven setting (°F) | Exact Celsius (°C) |
|---|---|
| 275 °F | 135 °C |
| 300 °F | 148.9 °C |
| 325 °F | 162.8 °C |
| 350 °F | 176.7 °C |
| 375 °F | 190.6 °C |
| 400 °F | 204.4 °C |
| 425 °F | 218.3 °C |
| 450 °F | 232.2 °C |
How many decimals should you keep?
Match the precision of the answer to the precision of the input. A weather report in whole degrees needs a whole-degree answer, so 77 °F is 25 °C.
A lab reading such as 98.6 °F deserves one decimal place. When you chain conversions, for example Fahrenheit to Celsius to Kelvin, keep at least two extra digits until the final step and round only once at the end, so errors do not pile up.
Check your answer in reverse
The easiest way to catch a slip is to convert your Celsius result back. Take 20 °C, multiply by 1.8 and add 32: you land on 68 °F, the number you started with. If the round trip does not return the original value, one of the steps was wrong.
Frequently asked questions
What is the formula to convert Fahrenheit to Celsius?
Subtract 32 from the Fahrenheit temperature and multiply by 5/9. In symbols, °C = (°F − 32) × 5/9.
What is 0 °F in Celsius?
0 °F is about −17.78 °C. Subtract 32 to get −32, then multiply by 5/9.
Are Fahrenheit and Celsius ever equal?
Yes, at −40. At that point −40 °F and −40 °C describe the same temperature.
Why is the conversion factor 5/9?
Between water’s freezing and boiling points there are 180 Fahrenheit degrees but only 100 Celsius degrees. 100/180 simplifies to 5/9.
Is 5/9 the same as 0.55?
Not exactly. 5/9 is 0.5555…, a repeating decimal. Rounding to 0.55 introduces a small error, so use the fraction or at least 0.5556.
How do I convert Fahrenheit to Celsius in my head?
Subtract 30 and halve the result. It is only approximate and drifts further from the true value as the temperature rises, so do not use it for cooking or science.
Sources
- Britannica: Fahrenheit temperature scale (britannica.com)
- Britannica: Celsius temperature scale (britannica.com)
- Omni Calculator: Fahrenheit to Celsius (omnicalculator.com)
