The formula, and a shortcut you can do in your head
Subtract 32, then multiply by 5/9 (or divide by 1.8). The order matters: subtract 32 before you scale, never after. For a quick estimate, subtract 30 and halve it: 72 F → (72 − 30) ÷ 2 = 21 C, within a degree or two of the exact 22.2. Every 18 F is exactly 10 C.
Weather, in 10-degree steps
| °F | °C | Feels like |
|---|---|---|
| 0° | −17.8° | Extreme cold |
| 32° | 0° | Freezing point |
| 50° | 10.0° | Light jacket |
| 68° | 20.0° | Room temperature |
| 77° | 25.0° | Warm |
| 90° | 32.2° | Hot |
| 100° | 37.8° | Heatwave |
Body temperature and oven settings
| What | °F | °C |
|---|---|---|
| Normal body temperature | 98.6° | 37.0° |
| Fever threshold | 100.4° | 38.0° |
| Water boils | 212° | 100° |
| Oven – moderate (cakes) | 350° | 177° |
| Oven – hot (roasting) | 428° | 220° |
| Oven – pizza | 450° | 232° |
US recipes give oven temperatures in Fahrenheit, European ones in Celsius. Setting a dial to 350 C instead of 350 F means nearly twice the heat, so check which scale a recipe uses before you preheat.
Two things people get wrong
- A change is not a reading. A drop of 20 F is a drop of about 11 C, not 20 C, because one Celsius degree equals 1.8 Fahrenheit degrees. Converting a difference is not the same as converting a temperature.
- 98.6 F is a rough average. That figure comes from an 1868 study. Modern data puts the average nearer 97.9 F (36.6 C), with a normal range of about 97.3 to 98.2 F.
Common questions
How do I convert Fahrenheit to Celsius?
Subtract 32, then multiply by 5/9 (the same as dividing by 1.8). For example, 72 F is (72 minus 32) times 5/9, which is 22.2 C. Always subtract 32 first, then scale.
What is 100 F in Celsius?
100 F is 37.8 C, just below the 38 C threshold that counts as a fever. It is close to normal body temperature, not dangerously hot.
At what temperature are Fahrenheit and Celsius the same?
At minus 40. It is the one point where the two scales read the same number: minus 40 F equals minus 40 C. It falls straight out of the algebra, not by design.
