Introduction
Try it now: use our free Celsius to Fahrenheit Converter to get the answer in seconds.
A friend once sent me a cake recipe from an American blog with one line underlined three times: “Bake at 350 degrees.” She baked it at what she thought was close enough, guessed a setting on her Celsius oven, and pulled out something that was somehow burnt on top and raw in the middle.
The problem was not her baking. It was the guess. 350°F is 176.7°C, usually rounded to 180°C on a home oven. Guess 200°C instead and a sponge pays for it.
Temperature is probably the conversion people meet most often — in recipes, weather forecasts on holiday, and instructions for everything from baby bottles to car engines. The good news is there are only two formulas, and once you have used them a few times on real numbers, they stop feeling like school maths.
The two formulas, plain and simple
To go from Celsius to Fahrenheit:
°F = °C × 9/5 + 32
In words: multiply the Celsius figure by 9, divide by 5, then add 32. If dividing by 5 feels awkward, multiply by 1.8 instead. It gives exactly the same answer, and most people find 1.8 easier on a phone calculator.
To go the other way, from Fahrenheit to Celsius:
°C = (°F − 32) × 5/9
Here the order matters more. Take 32 off first, then multiply by 5 and divide by 9.
Why the 32 at all? The two scales do not start at the same point. Water freezes at 0°C but at 32°F, and it boils at 100°C but at 212°F. That offset is the reason a straight multiplication never works, and it is also the step people forget most often.
Worked example: an oven at 180°C
Let us use the temperature from that cake, but in the direction most of us in Europe and the UK actually need.
You have a recipe that says 180°C. An American friend asks what that is in Fahrenheit.
- Multiply 180 by 9: 1,620
- Divide by 5: 324
- Add 32: 356
So 180°C is 356°F. Most US recipes would simply write 350°F, because oven dials are not laboratory instruments and a few degrees either way rarely ruins dinner. A fan oven is a separate matter — many cooks drop the temperature by about 20°C for fan, whichever scale they are using.
Now the reverse. A US recipe says 400°F for roast potatoes.
- Take off 32: 400 − 32 = 368
- Multiply by 5: 1,840
- Divide by 9: 204.4
Set your oven to 200°C or 205°C and you are fine.
Weather temperatures worth memorising
You do not need a formula for every forecast. A handful of anchor points cover most days:
- 0°C = 32°F — freezing, wrap up
- 10°C = 50°F — a cool spring day
- 20°C = 68°F — pleasant room temperature
- 25°C = 77°F — warm, t-shirt weather for most people
- 30°C = 86°F — properly hot
- 37°C = 98.6°F — normal body temperature
- 40°C = 104°F — a heatwave, or a fever that needs attention
We find it helps to learn these in pairs you actually care about. If you travel to the US in summer, 86 and 95 (35°C) are the numbers that will come up. If you are checking a child with a thermometer that shows Fahrenheit, 98.6 and 100.4 (38°C) matter far more than any oven setting.
A rough shortcut for weather only
Outdoors, you can double the Celsius figure and add 30. 22°C becomes 74°F by this method; the exact answer is 71.6°F. Close enough to decide on a jacket. Never use this shortcut for cooking, medicine or anything with a thermostat — that two or three degrees stops being harmless there.
Mistakes that catch people out
Forgetting the 32. If you just multiply 20°C by 1.8 you get 36, and you might think a mild day is near freezing in Fahrenheit. The real answer is 68°F.
Adding 32 at the wrong end. Going from Fahrenheit to Celsius, people often multiply first and subtract later. That changes the answer completely. Subtract first, always.
Trusting a body-temperature reading without checking the scale. A thermometer showing 99 might look alarming if you assume Celsius, and perfectly normal in Fahrenheit. Check the little letter on the display before you panic.
Gas marks. Older British recipes use Gas Mark numbers, which match neither scale. Gas Mark 4 is 180°C / 350°F, Gas Mark 6 is 200°C / 400°F. Converting a gas mark as if it were a temperature is a very common way to undercook a Sunday roast.
Questions people actually ask
“Is 25 degrees hot in Fahrenheit terms, or am I reading it wrong?”
You are probably reading a Celsius figure. 25°C is 77°F, a warm day. 25°F, on the other hand, is about −3.9°C — below freezing.
My oven only goes up in tens. Do I round up or down?
Round to the nearest marked setting. For cakes, round down slightly if you must choose; ovens tend to run hot and you can always give a cake two more minutes, but you cannot un-bake one.
Why does minus 40 keep coming up in videos?
Because −40 is the one point where the scales meet. −40°C and −40°F are the same temperature, which is a neat check: put −40 into either formula and you get −40 back.
Conclusion
Keep the two formulas somewhere you will see them — a note on the fridge works better than a bookmark you will never open. Multiply and add 32 going to Fahrenheit, subtract 32 first coming back. Learn the few weather anchors that matter in your life, use the rough shortcut only outdoors, and stop guessing with ovens. That cake, by the way, worked perfectly the second time, at 180°C.
Quick conversion table
| Celsius (°C) | Fahrenheit (°F) |
|---|---|
| −10 | 14 |
| 0 | 32 |
| 10 | 50 |
| 20 | 68 |
| 25 | 77 |
| 30 | 86 |
| 37 | 98.6 |
| 40 | 104 |
| 100 | 212 |
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