How Celsius and Fahrenheit are calculated
The two scales start in different places and use different degree sizes, so converting is one multiplication and one addition.
°F = °C × 9/5 + 32, and °C = (°F − 32) × 5/9
- Multiply your Celsius figure by 9/5, then add 32, and you have Fahrenheit. To go back, subtract 32 first, then multiply by 5/9.
- The scales are anchored on water: it freezes at 0 °C and 32 °F, and boils at 100 °C and 212 °F at sea level.
- They cross at −40, so minus forty degrees is the same temperature whichever scale you read.
- Kelvin uses the same size degree as Celsius but starts at absolute zero, so add 273.15 to a Celsius reading.
Worked example — 100 °C × 9/5 + 32 = 212 °F, the boiling point of water at sea level.
Common temperatures
| Celsius | Fahrenheit | Kelvin | You know it as |
|---|---|---|---|
| -273.15 °C | -459.67 °F | 0 K | Absolute zero |
| 0 °C | 32 °F | 273.15 K | Water freezes |
| 37 °C | 98.6 °F | 310.15 K | Normal body temperature |
| 35 °C | 95 °F | 308.15 K | A hot day |
| 180 °C | 356 °F | 453.15 K | Moderate oven |
| 100 °C | 212 °F | 373.15 K | Water boils |
Swipe the table sideways to see the rest.
Oven figures are for a conventional oven.
Things to consider
- For a quick estimate, double the Celsius figure and add 30. 25 °C becomes about 80 °F, against the exact 77 °F.
- Dishes from another country usually need the scale checked before you set the oven. 180 °C is 356 °F, not 180 °F.
- A fever reads differently on each scale: 38 °C and 100.4 °F are the same point.
- Thermometers and weather apps switch scale by region, so check which one you are reading before comparing two figures.
Frequently asked questions
How do I convert Celsius to Fahrenheit?
Multiply by 9/5 and add 32. 20 °C is 68 °F.
How do I convert Fahrenheit to Celsius?
Subtract 32, then multiply by 5/9. 68 °F is 20 °C.
Is 100 °C the same as 212 °F?
Yes. Both are the boiling point of water at sea level.
Where do Celsius and Fahrenheit match?
At −40. Minus forty degrees is the same temperature on both scales.
What is normal body temperature in Fahrenheit?
About 37 °C, which is 98.6 °F.
Results are estimates for general information only, not financial, medical or professional advice.