Fahrenheit to Celsius Converter
Type in either box. °C = (°F − 32) ÷ 1.8 — subtract before you divide.
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Taking 32 off first, and why the order matters
Going from Fahrenheit to Celsius reverses two operations, and they have to be undone in the opposite order to the way they were applied. Fahrenheit is built from Celsius by stretching the degree and then shifting the zero. To come back you shift first and stretch second.
°C = ( °F − 32 ) ÷ 1.8
Subtracting the 32 answers the question “how far above freezing is this, in Fahrenheit degrees?” Dividing by 1.8 then re-expresses that gap in the larger Celsius degrees. Divide before subtracting and the answer is wrong by about 18 degrees — a mistake that is easy to make and easy to catch, because the result comes out implausibly warm.
The division is often written as multiplying by 5/9, which is the same operation. Five ninths is 0.5556, so a Fahrenheit degree is a little over half the size of a Celsius one. That is worth holding on to: whenever you convert Fahrenheit to Celsius the number should get noticeably smaller, and if it does not, something has gone wrong.
The working, step by step
Every line updates with whatever you type above. Temperature is the one conversion where the method genuinely matters, because two things change at once: the size of a degree and the position of zero.
Why it is a line that misses the origin
Plotting one scale against the other shows the whole relationship at a glance. The slope is the size of a degree. The height at which the line crosses the vertical axis is the offset — the reason multiplying alone never works. Converting kilograms to pounds gives a line through (0, 0); this one does not.
The same temperature, two different numbers
One physical temperature, read off two scales. The tick marks are spaced differently and shifted along, which is exactly what the two numbers in the formula are doing.
Where does that sit?
A reading is easier to judge against temperatures you already know.
Your turn
Reading a method and being able to use it are different things. Answer within half a per cent and it counts as correct.
Score: 0 of 0
How to use this converter
- Type into either box. The other side updates as you go. There is no button to press.
- Negative readings are fine. Type a minus sign and the graph and scale below follow the value below zero.
- Swap the direction with the button between the boxes if you want to work the other way round.
- Set the decimals if the default is more or less precision than you need.
- Copy the answer with its unit, ready to paste.
- Share the result. The address bar tracks what you type, so the link you copy opens on the same reading.
If you enter something colder than absolute zero, the tool will say so rather than quietly converting a temperature that cannot exist.
Common uses and tips
Where this comes up
- Reading American weather. The 70s are pleasant, the 80s warm, the 90s uncomfortable. In Celsius that is roughly 21–26, 27–32 and 32–37.
- American recipes. 350 °F is 177 °C and everyone writes 180. 400 °F is 204 °C and gets written as 200. Round to the nearest ten.
- Medical readings. 100.4 °F is the usual fever threshold, which is exactly 38 °C — another case where the odd-looking decimal is a rounded Celsius figure in disguise.
- Pool and bath temperatures. A pool at 82 °F is 28 °C; a bath at 104 °F is 40 °C.
- Equipment ratings. Datasheets written for the American market often give operating ranges in Fahrenheit. A −40 to 185 °F range is −40 to 85 °C, which is the standard industrial band.
A shortcut worth knowing
Subtract 30 and halve. For 68 °F that gives 19 °C against a true 20. It runs about a degree low through the comfortable range and drifts further at the extremes, so treat it as a way of knowing whether to take a coat, not as a conversion.
Mistakes worth avoiding
- Divide last, not first. Subtract the 32 before dividing. Doing it the other way round is the single most common error in this direction.
- Differences use only the division. A drop of 18 °F is a drop of 10 °C. Do not subtract 32 from a change in temperature.
- Negative Fahrenheit is very cold. −10 °F is −23 °C. Fahrenheit readings below zero are rare enough in everyday life that the Celsius figure often surprises people.
Readings people look up most
Each one opens the converter with the number already in it.
- -40 °F to °C
- 0 °F to °C
- 20 °F to °C
- 32 °F to °C
- 40 °F to °C
- 50 °F to °C
- 60 °F to °C
- 68 °F to °C
- 70 °F to °C
- 72 °F to °C
- 75 °F to °C
- 80 °F to °C
- 85 °F to °C
- 90 °F to °C
- 98.6 °F to °C
- 100 °F to °C
- 100.4 °F to °C
- 165 °F to °C
- 212 °F to °C
- 350 °F to °C
Quick reference
| Fahrenheit | Celsius | Usually this is… |
|---|---|---|
| −40 °F | −40 °C | the point both scales agree |
| 0 °F | −17.8 °C | home freezer |
| 32 °F | 0 °C | water freezes |
| 50 °F | 10 °C | cool day |
| 68 °F | 20 °C | room temperature |
| 72 °F | 22.2 °C | typical thermostat setting |
| 86 °F | 30 °C | hot day |
| 98.6 °F | 37 °C | body temperature |
| 100.4 °F | 38 °C | fever threshold |
| 165 °F | 73.9 °C | safe for poultry |
| 212 °F | 100 °C | water boils |
| 350 °F | 176.7 °C | moderate oven (written 180) |
Questions people ask
What is the formula for Fahrenheit to Celsius?
Subtract 32, then divide by 1.8. As a fraction, °C = (°F − 32) × 5/9.
Why subtract before dividing?
Because the 32 was added last when the reading was built, so it has to come off first. Dividing before subtracting gives an answer roughly 18 degrees too high.
What is 350 °F in Celsius?
176.7 °C, which every recipe writes as 180 °C. Oven dials are marked in steps far coarser than three degrees.
What is a fever in Celsius?
The usual threshold of 100.4 °F is exactly 38 °C. The awkward decimal in the Fahrenheit figure is a converted round Celsius number.
Is 0 °F the coldest possible temperature?
No. It is −17.8 °C, an ordinary winter night in much of the world. The coldest possible temperature is absolute zero, −459.67 °F.