Temperature formulas
| From | To | Formula |
|---|---|---|
| Celsius | Fahrenheit | °F = °C × 9/5 + 32 |
| Fahrenheit | Celsius | °C = (°F − 32) × 5/9 |
| Celsius | Kelvin | K = °C + 273.15 |
| Kelvin | Celsius | °C = K − 273.15 |
Useful temperatures
| What | Celsius | Fahrenheit |
|---|---|---|
| Water freezes | 0 °C | 32 °F |
| Normal body temperature | 37 °C | 98.6 °F |
| Fever | 38 °C | 100.4 °F |
| Hot summer day in Lahore | 45 °C | 113 °F |
| Water boils (sea level) | 100 °C | 212 °F |
Why you can’t just multiply
Temperature scales start at different points: 0 °C is where water freezes, but on the Fahrenheit scale that point is 32 °F. So you multiply by 1.8 and add 32. Kelvin starts at absolute zero, the coldest anything can be, so it never goes below 0 K and is the scale used in physics and chemistry formulas.
A quick mental estimate for Celsius to Fahrenheit is “double it and add 30”: 25 °C gives 80 °F, close to the exact 77 °F.
Converting a temperature difference is different: a rise of 10 °C is a rise of 18 °F (no +32).