Fahrenheit to Celsius made painless
You read a US recipe, a US weather report, or a thermometer from an American drugstore, and now you need the number in Celsius like the rest of the world uses. The conversion is short, but it’s easy to fumble because you have to subtract before you scale.
The rule: C = (F - 32) x 5/9. Subtract 32 first, then multiply by 5/9 (about 0.5556). Enter a Fahrenheit value and the Celsius reading appears as you type. Use the dropdown to reverse it or bring in Kelvin.
Order of operations matters here
This is the spot people get wrong. You must subtract 32 before multiplying, not after. Fahrenheit’s zero point isn’t water freezing (that’s 32F), so you remove that 32-degree offset first to line the scales up, then shrink by 5/9 because a Fahrenheit degree is smaller than a Celsius one.
Flip the order and the answer is nonsense. (F - 32) then x 5/9, every time. The tool does it correctly so you don’t have to babysit the parentheses.
Temperatures worth memorizing
| Fahrenheit | Celsius | What it is |
|---|---|---|
| -40 F | -40 C | the crossover point |
| 0 F | -17.8 C | a properly cold winter day |
| 32 F | 0 C | water freezes |
| 50 F | 10 C | light jacket weather |
| 68 F | 20 C | room temperature |
| 98.6 F | 37 C | normal body temperature |
| 212 F | 100 C | water boils at sea level |
Three of these carry most of the load. Freezing at 32F is 0C. Room temp at 68F is 20C. Body temp at 98.6F is 37C. Anchor to those and you can sense the rest without a calculator.
When this saves you
Weather from the US is the everyday case. A forecast of 75F means little to a Celsius native until it becomes a pleasant 24C. A “100F scorcher” headline is 37.8C, genuinely hot.
Cooking is a frequent one too. American recipes give oven temps in Fahrenheit, but ovens sold in metric countries use Celsius. A 375F recipe is about 190C, and 425F is roughly 220C. Convert before you preheat or the timing won’t match.
Health readings round it out. A thermometer bought in the US shows Fahrenheit, and 100.4F is the classic fever threshold, which lands at 38C. Knowing that tells you whether a temperature is worth acting on.
Estimate it in your head
For a fast guess, reverse the trick used the other way: subtract 30 from the Fahrenheit value, then halve it. 70F minus 30 is 40, halved is about 20C (the exact answer is 21.1). It’s a little loose, but plenty good for deciding whether you need a coat. For cooking or medical use, trust the precise formula the converter applies.
It’s client-side JavaScript on your machine. Nothing you type leaves the device, and it keeps working with no connection once loaded.
FAQ
What’s the Fahrenheit to Celsius formula?
C = (F - 32) x 5/9. Subtract 32 first, then multiply by 5/9. So 50F is 10C.
What is 98.6F in Celsius?
Exactly 37C, normal human body temperature. The fever threshold of 100.4F is 38C.
Why do I subtract 32 before multiplying?
Because Fahrenheit’s freezing point is 32, not 0. Removing the 32 lines the scales up before you rescale, so the math comes out right.
Is there a temperature that’s the same in both scales?
Yes, -40. It reads -40 in Fahrenheit and -40 in Celsius.
Does this send my data anywhere?
Nope. The math is handled by JavaScript right on the page, so nothing is uploaded.